
Class \ ' .4 5 

Book . S T5 

GqpigM? 



COPYRIGHT DEPOSIT. 



A TEXT-BOOK 

ON 

ROADS AND PAVEMENTS 



BY 
FREDERICK P. SPALDING 

PROFESSOR OF CIVIL ENGINEERING, UNIVERSITY OF MISSOURI, MEMBER 
AMERICAN SOCIETY OF CIVIL ENGINEERS 



THIRD EDITION, REVISED AND ENLARGED 
FIRST THOUSAND 



NEW YORK 

JOHN WILEY & SONS 

London: CHAPMAN & HALL, Limited 

1908 






|UBftARYof CONGRESS, 
two Oooies tteci: 



OCT i i*ra 

0U\S&'°- AAC Nw. 
j OOHY J. 



Copyright, 1894, 1902, 1908, 

BY 

FREDERICK P. SPALDING 



Stanbope ipress 

F. K. GILSON COMPANY 
BOSTON. U.S.A. 



^ 



X 



K 



PREFACE. 



Successful practice in the construction of highways 
must depend upon correct reasoning from elementary 
principles in each instance rather than upon following 
definite rules or methods of construction. 

The aim of this book is to give a brief discussion, 
from an engineering standpoint, of the principles 
involved in highway work, and to outline the more 
important systems of construction, with a view to 
forming a text which may serve as a basis for a syste- 
matic study of the subject. 

Details and statistics of particular examples have 
for the most part been excluded as undesirable in a 
book of this character. Such information is available 
in many forms for those having the necessary elemen- 
tary training and experience to enable them to properly 
use it. 

Considerable space has been given to the location 
and construction of country roads, as seemed proper 
in view of the present general public interest in the 
matter, and the probable development of this new field 
of activity in engineering work. The improvement of 
our common roads must come through transferring 
such work to the charge of those who make it a profes- 
sion, and not through teaching the public how roads 
should be constructed. 

F. P. S. 
Ithaca, N.Y., July, 1894. 



m 



NOTE TO THIRD EDITION. 



The methods employed in the construction and 
maintenance of highways have changed so greatly 
since the first publication of this book that, in the 
preparation of this edition, it has been found necessary 
to practically rewrite the entire book. 

An effort has been made to briefly represent the best 
recent practice in highway work, and the book has 
necessarily expanded considerably beyond its former 
limits. 

F. P. S. 

Columbia, Mo., July, 1908. 



CONTENTS. 



CHAPTER I. 
Road Economics and Management. 

PAGE 

Art. i. Object of Roads i 

2. Resistance to Traction , 3 

3. Tractive Power of Horses 8 

4. Benefits Derived from Good Roads 10 

5. Cost of Wagon Transportation 12 

6. Economic Value of Road Improvement 16 

7. Sources of Revenue for Road Improvement 19 

8. Systems of Road Management , . . . , , . . . 2-2 

CHAPTER II. 
Drainage of Streets and Roads. 

Art. 9. Necessity for Drainage 26 

10. Surface Drainage 28 

11. Sub-drainage 29 

12. Tile Drains ^ 

13. Stone Drains 36 

14. Culverts „ 38 

15. Concrete Culverts 45 

CHAPTER III. 
Location of Country Roads. 

Art. 16. Considerations Governing Location 49 

17. Length of Road 52 

18. Rise and Fall 55 

19. Rate of Grade , 57 

20. Examination of Country * 59 

21. Placing the Line ...*... 63 

22. Comparison of Routes 65 

23. Changing Existing Locations 69 

vii 



Vlll CONTENTS. 

CHAPTER IV. 
Improvement and Maintenance of Country Roads. 

PAGB 

Art. 24. Nature of Improvements 72 

25. Grade and Cross-section 73 

26. Earthwork 79 

27. Earth Roads 85 

28. Gravel Roads 93 

29. Oiled Roads 96 

30. Sand-clay Roads 107 

31. Miscellaneous Roads 111 

32. Width of Tires 115 

CHAPTER V. 
Broken-Stone Roads. 

Art. 33. Definition 117 

34. Macadam Roads 118 

35. Telford Foundations 120 

36. Rocks for Road Building 124 

37. Methods of Testing Stone. 137 

38. Road Metal 146 

39. Compacting the Road 150 

40. Thickness of Road Covering 153 

41. Maintenance of Broken-Stone Roads.. 155 

42. Bituminous Macadam . . 159 

CHAPTER VI. 
Foundations for Pavements. 

Art. 43. Preparation of Road-bed 167 

44. Trenches in Streets. 168 

45. Purpose of Foundation , 170 

46. Bases of Gravel and Broken Stone 172 

47. Concrete Bases 172 

48. Bituminous Foundations 175 

49. Miscellaneous Foundations 176 

50. Choice of Foundations. 178 



CONTENTS. IX 

CHAPTER VII. 
Brick Pavements. 

PAGE 

Art. 51. Paving Brick 180 

52. Tests for Paving Brick 187 

53. Construction of Brick Pavements 201 

54. Filling the Joints 206 

55. Maintenance of Brick Pavements 211 

CHAPTER VIII. 

Bituminous Pavements. 

Art. 56. Asphalt 214 

57. Surface Mixtures 225 

58. Tests for Asphalt Cement 231 

59. Construction of Sheet Pavement 243 

60. Asphalt Blocks 248 

61. Maintenance of Asphalt Pavements 249 

62. Bitulithic Pavements 252 

CHAPTER IX. 
Wood-Block Pavements. 

Art. 63. Types of Wood-block Pavement 258 

64. Wood Blocks 262 

65. Treatment of Wood Blocks 265 

66. Tests for Wood Blocks 270 

67. Construction of Wood-block Pavements 272 

68. Maintenance of Wood-block Pavements 276 

CHAPTER X. 

Stone-Block Pavements. 

Art. 69. Stone for Pavements 278 

70. Cobblestone Pavements 280 

71. Belgian Blocks 281 

72. Granite and Sandstone Blocks 282 

73. Construction 284 

74. Stone Trackways 287 



X CONTENTS. 

CHAPTER XL 

City Streets. 

PAGE 

Art. 75. Arrangement of City Streets 289 

76. Width and Cross-section 294 

77. Street Grades 299 

78. Street Intersections 302 

79. Footways 304 

80. Curbs and Gutters 310 

81. Crossings 316 

82. Street-railway Track 317 

83. Trees for Streets 330 

84. Selection of Pavements 331 

85. Sources of Revenue for Street Improvement 338 



ROADS AND PAVEMENTS. 



CHAPTER I. 

ROAD ECONOMICS AND MANAGEMENT. 
Art. i. Object of Roads. 

The primary object of a road or street is to provide 
a way for travel, and for the transportation of goods 
from one place to another. The facility with which 
traffic may be conducted over any given road depends 
upon the resistance offered to the passing of vehicles 
by the surface or the grades of the road, as well as 
upon the freedom of movement allowed by the width 
and form of the roadway. In order that a road may 
offer the least resistance to traffic, it should have as 
hard and smooth a surface as possible, while affording 
a good foothold to horses, and should be so located as 
to give the most direct route with the least gradients. 

The expediency of any proposed road construction 
or improvement depends upon its desirability as affect- 
ing the comfort, convenience, and health of residents 
of the locality, and also upon its economic value, which 
is largely determined by its cost and durability, as well 
as upon the facility it gives for the conduct of traffic. 

The desirability of a road surface for any particular 
use depends both upon its fitness for the service 
required of it and upon its durability in use. 



2 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Upon a country road, the problem of improvement 
ordinarily consists simply in providing the hardest and 
most durable surface consistent with an economical 
expenditure of available funds, the object being to 
lighten the cost of transportation by reducing the 
resistance to traction, and to render travel easy and 
comfortable. 

Upon city streets, however, several other factors 
may be of importance in the design of highway 
improvements. 

The comfort both of those using the street and of 
the occupants of adjoining property will be largely 
affected by the freedom of the surface from noise and 
dust. 

The safety of the pavement in use, its effect upon 
the health of residents of the locality, and its economic 
value must in each case be considered. 

To adjust to the best advantage these various ele- 
ments, frequently quite discordant with each other, is 
a matter which can only be accomplished by the exer- 
cise of good judgment. Local conditions and necessi- 
ties must always be considered — such as the difficulties 
of drainage, the availability of various materials, the 
nature of the traffic to be carried, and the needs of the 
business or property interests of the neighborhood. 
Thus, for heavy hauling of a large city, the durability 
and resistance to wear of the pavement may be the 
paramount consideration; for an office district, quiet 
may be very important; for the lighter driving of a 
residence street, the elements of comfort and health- 
fulness may properly be considered as of greater force 
than the purely economic ones; while in all of the 
cases the necessary limitation of first cost will largely 
determine what may or may not be done. 



ROAD ECONOMICS AND MANAGEMENT. 3 

The problem of the highway engineer, in designing 
works of this character, involves the consideration of 
these various elements and their proper adjustment to 
give the best results. 

The kinds of road surface most commonly employed 
are as follows: For the streets of cities and towns, 
pavements of stone blocks, brick, asphalt, and wood; 
for suburban streets and important country roads, 
macadam and gravel surfaces; for ordinary country 
roads in general, surfaces of earth or gravel. 

Art. 2. Resistance to Traction. 

The resistance to traction of a vehicle on a road 
surface may be divided into three parts: axle friction, 
rolling resistance, and grade resistance. 

Axle friction varies with the nature of the bearing 
surfaces, and for vehicles of similar construction is 
directly proportional to the load. It is entirely inde- 
pendent of the nature of the road surface. 

Rolling resistance is of two kinds : that due to irregu- 
larities in the surface of the road, and that of a wheel 
to rolling upon a smooth surface, sometimes called 
rolling friction. 

The resistance due to an inequality in the road sur- 
face is the horizontal force necessary, at the axle, to 
raise the weight upon the wheel to the height of the 
obstacle to be passed. Thus (Fig. 1), by the principle 

Q 

of the lever, P = W - • 

a 

For small inequalities, this resistance will be approxi- 
mately inversely as the diameter of the wheel. The 
effect of small irregularities in the surface, however, 
is due more to the shocks and concussions produced by 




4 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

them than to the direct lifting action of the obstacle, 
and the resistance due to uneven surface is greater at 

high than at low velocities. 

Rolling friction is probably due 
for the most part to the compres- 
sibility of the surface of the road, 
which permits the wheel to indent 
it to some extent. The wheel is 
thus always forcing a wave of the 

surface before it, or climbing an 
Fig. i. .... , , . . 

inclination caused by its weight 

upon the road surface. 

Size of Wheels. — The resistance to traction varies 
for wheels of differing diameters, being less for large 
than for small wheels. The experiments of M. Morin, 
in France, seemed to indicate that the resistance varies 
inversely as the diameter. Other experiments have 
indicated a less variation, approximately as the 
square root of the diameter, while Mr. D. K. Clark 
(Roads and Streets, by Law and Clark; London, 
1890) concludes, from a mathematical discussion based 
upon the assumption that the material of the surface 
is homogeneous and the pressure proportional to the 
depth of penetration, that the resistance to traction 
is inversely as the cube root of the diameter of the 
wheel. The experiments of Mr. Mairs (Bulletin, Uni- 
versity of Missouri Agricultural Experiment Station, 
1902) indicate that tractive resistance is somewhat 
less with large than with small wheels, being nearly 
inversely as the square root of the diameter, but as 
might be expected, differing somewhat for different 
road surfaces. 

For practical purposes it may be considered that, for 
wheels of ordinary sizes used on road vehicles, the 



ROAD ECONOMICS AND MANAGEMENT. 5 

rolling resistances are equal to the load multiplied 
by a coefficient which depends upon the nature 
and condition of the road surface, although these 
coefficients are somewhat affected by the sizes of the 
wheels. 

Width of Tire. — The effect upon tractive resistance 
of the width of tire upon the wagon wheels depends 
upon the character of the surface upon which the wheel 
is rolling. In a series of experiments at the University 
of Missouri Agricultural Experiment Station in 1897, 
it was found that wide tires considerably diminished 
tractive resistance upon broken stone and gravel roads, 
and upon earth roads in good condition, but upon 
muddy roads or when a hard road is covered with deep 
dust the resistance is greater for wide tires. The wide 
tire also has considerable advantage upon plowed 
land or sod, not cutting in so deeply. 

Speed of Travel. — Tractive resistances are somewhat 
greater at high than at low velocities. This difference 
is very slight on earth roads in good condition or on 
smooth pavements; but on rough pavements where con- 
cussions take place the resistance increases rapidly as 
the speed becomes greater. 

Road Surface. — Many experiments have been made 
for the purpose of determining the tractive force 
required for a given load upon various road surfaces. 
The results show somewhat wide variations, as would 
be expected when the many elements that may affect 
them are considered. The following table shows a 
few average results, which will give some idea of the 
relative resistances of various surfaces and of the 
advantage to be derived from a smooth and well-kept 
road surface: 



A TEXT-BOOK ON ROADS AND PAVEMENTS. 



TRACTIVE RESISTANCES ON VARIOUS SURFACES. 



Character of Road. 



Earth Roads — in fair condition . . . 

dry and hard 

Macadam — very good 

ordinary 

poor 

Granite block pavement — good 

ordinary 

Brick pavement 

Wood block pavement 

Asphalt pavement 



Resistance per 


Ton, 




Pounds. 


IOO 


to 


175 


60 to 


125 


25 


to 


50 


40 


to 


IOO 


75 


to 


150 


2 5 


to 


50 


40 


to 


80 


20 


to 


50 


25 


to 


So 


20 


to 


70 




The resistance upon asphalt is greater at high than 
at low temperatures. 

Grade Resistances. — Tractive resistance due to grade 
is independent of the nature of the road surface or of 

the size of the wheels. 
It is equal to the load 
multiplied by the sine 
of the angle made by 
the grade with the hor- 
izontal. Thus in Fig. 2 
the tractive force P, 
due to the grade, is the 
force necessary to pre- 
vent the wheel from rolling down the slope under the 
action of the weight W, or it is the component of W 
parallel to the slope ac. 

.:P = W*- 

ac 

Grades are ordinarily expressed in terms of rise or 
fall in feet per hundred, or as percentage of horizontal 
distance. 



Fig. 2. 



ROAD ECONOMICS AND MANAGEMENT. 7 

For all ordinary cases of small inclinations ab is 
approximately equal to ac, and we may take 

be 
P=W-; 
ab 

or the tractive force necessary to overcome any grade 
equals the load multiplied by the percentage of grade. 
The total tractive force necessary to haul a load up 
an inclined road equals the sum of the force necessary 
to haul the load upon the same surface when level and 
the force necessary to overcome the grade resistance. 
Thus, if we wish to find the tractive effort necessary to 
haul a load of 2 tons up a grade of 3 ft. in 1 00 over a 
good macadam road. Taking the resistance of the 
road surface when level at 60 lbs. per ton, we have for 
the total resistance 

R = 2 X 60 + 4000 X yf-Q = 240 lbs. 

In going down the grade, the force due to grade 
becomes a propelling force, and the tractive effort 
required is the difference between the surface resist- 
ance and grade force. In case the grade force be the 
greater, the resulting tractive force becomes negative, 
or it will be necessary to apply the force as a resistance 
to prevent acceleration of the velocity in the descent. 

The angle for which the tractive force required for a 
given surface equals the grade resistance is called the 
Angle of Repose for that surface. In the case given 
above, 2 X 60 — 4000 X yto = °> or tne an gl e of repose 
for a surface whose level resistance is 60 lbs. per ton is 
a 3 per cent grade. If a vehicle were left standing upon 
that inclination, it should remain standing with the 
forces just balanced. If it were started down the 
grade, it should continue to move at a uniform rate, 
without the application of any other force. 



8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 3. Tractive Power of Horses. 

The loads that a horse can pull upon various road 
surfaces will not necessarily be proportional to the 
resistance offered by the surface to traction, as the 
tractive force that the horse can exert depends upon 
the foothold afforded by the surface. The ability of a 
horse to exert a tractive force depends upon the 
strength of the animal, upon his training for the par- 
ticular work, and whether he be . accustomed to the 
surface upon which he is travelling. The work of dif- 
ferent animals is therefore subject to considerable varia- 
tions, and only very rough approximations are possible 
in giving average values of the work a horse may do 
under differing conditions. 

The tractive force that may be exerted by a horse, 
at moderate speeds, varies approximately inversely as 
the rate of speed; or, in other words, the power that 
a horse can exert through any considerable time is 
nearly constant for varying velocities. Thus it may 
be assumed, as an average value, that a horse working 
regularly ten hours per day can put forth a tractive 
effort of 80 pounds at a speed of 250 feet per minute 
on an ordinary level road surface. 

For the power of the horse we then have 

Power = force X velocity =80 X 250 = 20000 foot- 
lbs, per minute. 

For any other rate of speed, as 200 feet per minute, 
we would have 20000 -*- 200 =100 pounds as the 
tractive force exerted by the horse. 

If the period of daily work be lessened, the power 
that may be developed will be increased, either by 
increasing the load or the velocity. 



ROAD ECONOMICS AND MANAGEMENT. 9 

The tractive force that a horse is able to exert 
decreases very rapidly as the rate of inclination 
increases. This is due both to the expenditure of 
power by the horse in lifting his own weight up the 
grade, and to the less firm footing on the inclination. 
The effect of differences in the foothold afforded by 
various pavements is very marked in the loss of tractive 
power upon grades. 

In the table below are given the loads that an 
average horse may be expected to continuously haul 
up different inclinations, on various road surfaces, at 
slow speed. These figures, while of little value as an 
absolute measure of what may be done in any par- 
ticular case, are of use as a rough comparison of the 
relative tractive properties of different surfaces and 
grades. The effect of grades upon tractive effort will 
also depend upon the condition in which the surface is 
maintained, and upon the weather. Snow and ice in 
winter, or the damp and muddy condition of some 
pavements in wet weather, have a very considerable 
effect to diminish tractive power. 

LOADS IN POUNDS THAT A HORSE CAN DRAW UPON VARIOUS 
SURFACES AND GRADES. 



Kinds of Surface. 



Earth road — good 

poor 

Broken-stone — good . . . 

poor. . . 
Stone Blocks — good . . . 

poor. . . . 
Asphalt — clean and dry 







Rate of Grade 








1 in 


2 in 


3 in 


4 in 


5 in 


10 in 




100. 


IOO. 


IOO. 


IOO. 


IOO. 


IOO. 


3000 


2400 


2000 


1600 


1400 


I200 


800 


1300 


I IOO 


900 


700 


600 


500 


400 


4000 
1600 


2700 
I IOO 


2000 
800 


1600 
600 


1400 
500 


I200 

45° 


700 
2^0 


6000 


4500 


33°° 


2700 


2200 


1700 


900 


3000 
8000 


2300 
4000 


1700 
2500 


1400 
1800 


I IOO 

1300 


900 
1000 


45° 
400 



15 m 
100. 



300 

200 
IOO 

400 
200 



IO A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In general, the tractive effort that a horse may exert 
is approximately proportional to the weight of the 
horse and the averages above given correspond to light 
animals; many horses are capable of exerting double 
the pull mentioned. 

A horse may frequently exert for a short time a 
tractive force about double that which he can exert 
continuously; hence, when short grades occur steeper 
than the general grades of the road, loads may often 
be taken over them much heavier than could be carried 
if the steeper grade prevailed upon the road. 

On ordinary country roads in dry weather the 
amount of load that can be hauled is usually deter- 
mined rather by the grades than by the nature of the 
surface. Unless the gradients are very light the 
amount of load that can be carried on a broken-stone 
surface does not differ greatly from what may be taken 
on a dry and hard earth road. In improving a road 
by substituting a hard surface for a surface of earth 
the gradients and location should therefore always be 
carefully studied, with a view to deriving the full 
practical benefit from the hard surface in the light 
traction that it may require with easy ruling gradients. 

Art. 4. Benefits Derived from Good Roads. 

The condition of the public highways is a matter of 
the most vital interest to any rural community. Upon 
it depends largely the social life and enjoyment of the 
people living in the country as well as the ability to 
market the products of the farm to the best advantage. 

In nearly all parts of the country the roads are fairly 
good during a portion of the year; but there is also 
usually a period when they are very bad, in very 



ROAD ECONOMICS AND MANAGEMENT. II 

many localities becoming practically impassable. The 
improvement of the road surfaces and the use of 
systematic maintenance would make the roads better 
at all times, making it possible to haul larger loads 
over them and rendering them more pleasant to travel; 
but the most important object of road improvement is 
to eliminate the period when roads are not in condition 
to use and make it possible to drive upon them and 
haul loads over them at all times. 

The benefits of good roads may be classified as social, 
educational, and financial. They promote social inter- 
course .among the residents of a country district by 
making travel easy and pleasant. Where the roads 
become impassable during a portion of the year, the 
residents are practically isolated at the period of 
greatest leisure and lose that intercourse with their 
neighbors which is a most important means of enjoy- 
ment and development. Attendance at church and 
public meetings is facilitated by good roads. There 
are many localities where the condition of the roads 
practically closes the churches during a considerable 
portion of each year, and in some instances they have 
been so deserted on this account as to be abandoned. 
The rural mail delivery also depends for its efficiency 
upon the good condition of the roads. 

The consolidation of rural schools and establish- 
ment of rural high schools, made possible by good roads, 
is an important advance in educational methods, and 
places rural communities more nearly on an equality 
with the cities in educational advantages offered to 
children. 

Roads which can be traveled all the year admit of 
marketing the products of the farm at any time which 
may be most advantageous, enabling the farmer to take 



12 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

advantage of favorable market conditions and prices, 
or to transport his products at a convenient season, 
when he can do the work without interference with 
other duties of men and teams. 

The condition of the highways has also considerable 
effect upon the business of the towns into which they 
may lead; where they are uniformly good throughout 
the year mercantile business will be better distributed 
between different seasons, and a larger volume of 
business will be transacted. The same effect is pro- 
duced upon railway transportation. Congestion in rail- 
way business and scarcity of cars is frequently the 
result of the hurried marketing of crops to take advan- 
tage of a good condition of the wagon roads, and a 
much better distribution of business might be obtained 
through an improved condition of the highways. 
The area tributary to a town or a railway may also 
frequently be considerably extended by road improve- 
ment. * 

The greatest benefits derived from good roads are in 
the increased comfort, convenience, and pleasure of the 
people living near them, and in the social and edu- 
cational advantages which they make possible and 
which add greatly to the attractiveness and happiness 
of rural life. 

Art. 5. Cost of Wagon Transportation. 

The effect of bad roads upon the cost of wagon 
transportation has been the subject of much discussion 
and many estimates have been made which have 
arrived at widely different conclusions. Many of 
these discussions have failed to take account of all the 
factors entering into the problem and have arrived at 



ROAD ECONOMICS AND MANAGEMENT. 1 3 

wildly extravagant results. Efforts have been made 
by the Road Inquiry Office of the United States 
Department of Agriculture to collect statistics con- 
cerning the volume and cost of hauling farm produce to 
market for the whole United States. These statistics 
include estimates of the average length of haul and the 
cost per ton-mile, with a view to basing upon them some 
conclusion as to the saving to the country in general 
which would result from the improvement of the roads 
so that larger loads may be carried, and less labor be 
required for moving the crops. Statistics of this kind 
are very difficult to gather, being altogether dependent 
upon the judgment of the man who collects them in 
each locality, and representing only very approximately 
the average conditions. They are of value as giving 
information concerning the traffic to which the roads 
are subject in various localities and the need for road 
improvement, but they do not contain data upon which 
any reasonable estimate can be based of the actual 
saving which might be effected by road improvement. 
Such general estimates are not of any particular value 
other than that of showing something of the size of the 
problem when applied to the whole country. 

Many palpably erroneous and exaggerated estimates 
of the saving in cost of transportation by road improve- 
ment have been published and have often seriously 
injured the cause of good roads. They aim to show 
the large saving which may be effected by the farmer 
through reducing the cost of moving his crops to 
market, but their fallacies are evident to the farmer 
who reads them and applies them to his own conditions, 
and in many instances lead him to doubt the good 
faith of the whole movement for good roads. These 
estimates commonly treat the subject as though the 



14 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

whole of the crops were hauled to market in full loads 
by teams kept by the farmers for that purpose alone, 
and which could be dispensed with if the roads were so 
improved as to require a less number of loads, and con- 
sequently less teams to transport the crops, which is 
clearly not the case. 

The effect of the condition of the highways upon 
the cost of wagon transportation depends upon the 
character of the traffic. Where this consists of the 
transportation of some product which is hauled in full 
loads, with teams which are employed for this purpose 
only, the cost of transportation is readily ascertained, 
and the saving due to any improvement which increases 
the load carried by each team may be found by esti- 
mating the cost of the decreased number of teams 
required. If an earth road in poor condition be re- 
placed by a good macadam surface, the load which 
can be taken over the road may easily be doubled if 
upon light gradients, while where a traffic of this 
character must be taken over an earth road in bad or 
muddy condition, the construction of an improved 
road surface may result in loads four or five times as 
heavy as before. In this case the number of teams is 
inversely proportional to the maximum load which may 
be hauled and the cost is proportional to the number 
of teams. This condition soemtimes, though rarely, 
occurs upon wagon roads, the traffic usually being of a 
mixed character, with varying percentages carried in 
full loads, and with teams kept for other purposes and 
only incidentally used for transportation upon the 
roads. 

For the purpose of estimating the cost of trans- 
portation upon ordinary country roads it is necessary 
to separate the traffic into classes and determine what 



ROAD ECONOMICS AND MANAGEMENT. 1 5 

portion of it is carried in full loads. This is always a 
matter of difficulty where the traffic is varied and 
can only be done in a very roughly approximate 
manner. The light portion of the traffic will, of course, 
be benefited by improved roads, but the saving in 
cost of conducting the traffic, while existent, is 
usually comparatively small and practically indeter- 
minate. It consists in saving time of men and teams 
through greater speed of travel, and in less wear 
upon teams and vehicles. When such traffic must be 
conducted over muddy and bad roads these items 
may be of considerable importance, although they can 
not be evaluated, but commonly they are of slight 
importance. 

The heavy portion of the traffic is more directly 
affected by the character of the roads over which it 
passes. This traffic is carried in full loads, which are 
limited in amount by the condition and gradients of the 
roads. In some localities this constitutes the main 
portion of the traffic; in others it is a comparatively 
small part of the whole. No generalization concern- 
ing the value of road improvement as reducing the cost 
of transportation can therefore be made with any 
approach to accuracy; but in a particular instance where 
data is obtainable concerning the heavy traffic, it is 
possible to roughly estimate the saving in labor of 
transportation through road improvement. If we 
can determine the cost of using teams for this purpose, 
an approximate estimate may also be made of the 
saving in cost of transportation through such improve- 
ment. The cost of using teams for highway trans- 
portation is often difficult to obtain on account of the 
fact that such teams are commonly kept for other 
purposes and only incidentally used for road work, 



1 6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and in some instances it is possible that the trans- 
portation is done when there is no other work which 
could be done by the team. In general, however, it is 
fair to assume that the cost of the work is proportional 
to its amount, and that if the teams were not employed 
in transportation on the highway, they would be other- 
wise usefully engaged. , In estimating the cost of work 
of teams, the actual cost to the farmer of keeping the 
team should be used and not the rental value of teams 
in the vicinity. 

A careful examination of the local conditions sur- 
rounding the traffic is essential to any reasonable 
estimate of saving to be effected in cost of transpor- 
tation upon highways. Such estimates are not of 
much value at best as giving actual amount of savings, 
but studies of this kind may be of value in giving a 
better conception of the economics of the good roads 
problem. 

Art. 6. Economic Value of Road 
Improvement. 

The value of a road improvement to a community 
and the amount of money that may reasonably and 
profitably be expended in the construction and main- 
tenance of common roads is a subject the discussion of 
which leads different persons to widely different con- 
clusions, depending upon the point of view and the data 
assumed. Any improvement, either in position or 
surface, that has the effect of increasing the loads that 
may be taken over a road by a given power lessens the 
number of loads necessary to carry the traffic, and 
effects a saving in time and labor of men and teams, 
which may reasonably be considered to have the same 



ROAD ECONOMICS AND MANAGEMENT. 1 7 

money value as the time used in the work. This has 
been discussed in Art. 5 and is the most direct and 
obvious financial gain which may result from road 
improvement. 

Saving in cost of transportation is not, however, 
the most important advantage to be gained by road 
improvement, and if it were the only one, in many 
instances, the expenditure of money necessary to 
secure better roads could not be justified as econom- 
ically profitable. 

It is in wet and muddy weather that improved 
surfaces have their chief advantage over earth roads, 
and the main object of introducing hard and imperme- 
able surfaces is to eliminate the period when ordinary 
earth roads are apt to be muddy and practically 
useless for the purposes of transportation, and to 
substitute a road that may be used at any season. 
Systematic drainage has a similar object. To a farm- 
ing community the economic advantage of a road 
uniformly good at all seasons is greater than might 
appear at first glance. It may in many instances 
amount practically to a saving equal to nearly the 
entire cost of hauling by permitting the work to be 
done at times when other work is impossible, thus 
making men and teams available for other duty in 
good weather. The ability to use a road at any 
season is also of advantage in the independence of 
weather that will make it possible to take advantage 
of the condition of the markets in the disposal of 
produce or purchase of supplies. These advantages 
may be of greater or less importance according to the 
character of the traffic carried by the road. In geperal, 
while they are indeterminate and can not be expressed 
in money value, they are evidently of more economic 



1 8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

importance than the saving effected in costs of trans- 
portation. 

The nature of the country roads affects the towns to 
which the country is tributary as well as the country 
itself. They directly affect trade in seasons of bad 
weather, both in regulating the demand for supplies 
for country consumption and in controlling the supply 
of produce which is available for market; indirectly 
also the prosperity of a rural district means that of its 
trade center. The improvement of country roads is, 
therefore, of direct economic value to towns into which 
they may lead, but this, like most of the other advan- 
tages of good roads, is dependent upon data which can 
not be accurately estimated. 

All of these points must be considered in any at- 
tempt to arrive at any proper conception of the advan- 
tages of a proposed improvement. In any particular 
case the local interests will determine the relative 
importance of the various elements, and a careful 
analysis of the trade that does pass over the road and 
that would pass over it under different conditions will 
enable a judgment to be formed as to the value of 
improvements. The attempt to base an estimate of 
the economic value of a proposed road improvement 
upon the prospect of direct financial return is, however, 
apt to be misleading and to leave out of account the 
most important benefits of such improvements. The 
social and educational benefits mentioned in Art. 4 
are of highest importance and have also an economic 
value in their effect upon the desirability of a locality 
as a place of residence. The economic importance 
of good roads is shown in their effect upon land values, 
which are largely affected by them. 

The money spent in road improvement is to be 



ROAD ECONOMICS AND MANAGEMENT. 1 9 

considered as an investment, which will return annual 
interest to the community in reduced costs of trans- 
portation, greater freedom of traffic and travel, and in 
the increased comfort and happiness of the people. 

Art. 7. Sources of Revenue for Road 
Construction. 

Various methods have been employed for securing 
the funds necessary for the construction and improve- 
ment of country roads. Many of the earlier roads in 
this country were toll roads built by private capital 
and kept up exclusively by charges paid by travelers. 
Toll roads are objectionable because they impose a 
tax upon all the traffic of the road, and also because 
the cost of management is usually large, thus restricting 
traffic. They are conducted for the purpose of deriving 
a profit from their operation. They are gradually 
disappearing and should be dispensed with except 
under exceptional circumstances. 

District Roads. The most common method of rais- 
ing funds for road purposes is by property and poll 
tax in small districts. By this method a small poll 
tax is assessed against each voter of the district, 
payable either in money or labor, and a certain property 
tax which is levied uniformly upon property in the 
district, and often also payable in labor or cash at the 
option of the property owner. In some instances 
the property tax must be paid in money, and in others 
a portion of it must be paid in money. In some poor 
and sparsely settled localities the poll tax is the 
principle source of revenue, and road work consists 
mainly in working out the road tax by the residents 
of the district. 



20 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

As a general thing, the results of the collection of 
road tax in labor are not good. Under the labor 
system men do not work on the roads a sufficient 
length of time to become expert enough to do good 
work; many of them feel no particular interest in the 
work and are only concerned in getting in the required 
time. Under this system it is not usually possible 
to have the road work done when it is needed, as the 
convenience of the laborers must be considered. In 
many places therefore efforts are being made to require 
the payment of- property tax in money. This is 
highly desirable wherever the money will be expended 
under proper management, but in numerous instances 
no improvement has followed a change to the cash 
system because of a lack of intelligent control of the 
work. 

County Road Tax. In some" states there is a general 
property tax for road and bridge purposes. This 
tax is, usually, at the disposal of the county commis- 
sioners, or county court, which uses it for the con- 
struction and maintenance of county bridges and also 
for such road work as may be of special importance and 
of interest to the county in general. Frequently 
such funds are used to encourage the construction of 
improved roads by paying a part of the cost where 
owners of property specially benefited, or road dis- 
tricts in which the road may lie, are willing to pay 
their share of the cost. The maintenance of the 
ordinary country roads usually depends upon the 
district tax, but a county road fund judiciously 
administered may do much to improve the more im- 
portant highways and thus secure good roads leading 
from various parts of the county to the market 
towns. 



ROAD ECONOMICS AND MANAGEMENT. 21 

Special Assessments. The laws of some of the 
states provide for levying special assessments against 
property benefited by the improvement of country 
roads. These laws are usually permissive, allowing 
either the county court or majority of property owners 
concerned, by instituting proper proceedings in court 
or before commissioners, to have the improvement 
made and assessed upon property within certain 
distances from the road. In some instances the 
whole cost is paid in this way; in others a part is 
appropriated by the county, or state, or both, and a 
part is raised by special assessment. 

State Appropriations., Several of the states appro- 
priate state funds, which may be used in assisting in 
the construction of improved roads throughout the 
state. The amount of assistance given varies in 
different states; in New Jersey 33^ per cent of the 
cost is paid by the state, 56! per cent by the. county, 
and 10 per cent by the abutting property; in Massachu- 
setts the state pays 75 per cent, and the county 25 per 
cent; in New York the state pays 50 per cent, the 
county 35 per cent, and the town 15 per cent. 

These various laws all have for their object the 
distribution of cost upon all interests benefited by 
the work. There has been much discussion of this 
subject and many opinions expressed concerning the 
justice of various methods of distributing the cost. 
The improvement of main roads by local districts 
without outside assistance does not seem equitable, 
and the use of general county tax for this purpose is 
intended to place a share of the cost upon the towns 
and other interests not reached in the local taxes. 
It also, secures a centralized and usually better control 
of road work. All of the sources of revenue are 



22 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

benefited by road improvement and may reasonably 
be expected to contribute to its cost, but the exact 
evaluation of relative benefits is not possible, and the 
amount each must pay should be determined by con- 
sidering what is feasible and in what way the greatest 
improvement may be effected. 

Art. 8. Systems of Road Management. 

Several different systems for managing the work of 
constructing and repairing country roads have been 
proposed or are in use in various places. These 
systems differ in the placing of the control of the roads 
and in the methods adopted for providing funds. 

The control of the roads under the various systems 
may be vested in the national government, in the vari- 
ous State governments, in county or parish organiza- 
tions or in townships or districts. In regard to the 
location of control and responsibility, it may be 
remarked that there are two points to be kept in view. 

1st. In order that the work may be economically 
conducted, the section of country included under one 
control should be sufficient to warrant the permanent 
employment of a man, or corps of men, whose business 
it shall be to continually look after the roads, study 
their needs, and systematically conduct their improve- 
ment. It should admit of the ownership and use of 
labor-saving machinery for the economical execution 
of the work, but should not be large enough to require 
an elaborate and complicated organization. 

2d. The control of road work should be so arranged 
that, as nearly as possible, all of the interests directly 
affected by the condition of any road shall have a 
voice in its management and contribute to its support. 



ROAD ECONOMICS AND MANAGEMENT. 23 

Common roads are essentially local in their character 
and are not usually employed as lines of continuous 
transportation over any considerable distance. They 
are not, therefore, of state or national importance as 
lines of communication, although as factors in the 
general welfare of the people they must, of course, like 
all other such factors, be of general interest and concern 
to both state and nation. 

The nation, and in most cases in this country the 
state, is too large a unit to assume direct control of 
road work. In general, the interests over so large an 
area are so varied, and the requirements so different, 
as to prevent a harmonious and successful organization 
of such work with a probability of economical adminis- 
tration. In some cases, however, such control might 
be wise and proper, and the recognition of the impor- 
tance of road improvement to the general welfare of 
the state, through the payment by the state of a 
portion of the cost of permanent improvements, has 
in some instances proved a powerful stimulus to local 
action. 

The control of road management by towns and small 
districts is nearly always inefficient because the organi- 
zation is too small to support a proper management 
or provide the necessary appliances for economic work. 
Under this system the man in charge of the roads is 
usually engaged in other work; he is not a road engineer, 
and can, and is expected to, give but little attention to 
the road work. This system of control is also usually 
unfair, except in case of roads intended for the accom- 
modation of the local district only. For instance, a 
road passing through a town may be a thoroughfare 
for the towns upon each side. The principal traffic 
may be this through-trade to points beyond the limits 



24 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of the town in which the road is situated. The cost of 
keeping up this road is largely due to outside traffic, 
and the intermediate town should not be required to 
bear all the expense of maintenance. On the other 
hand, the interests of the towns whose trade passes 
over the road are largely affected by its nature, and 
the people of these towns should be permitted a voice 
in determining the character of the road. Most of the 
more important roads of every vicinity pass thus 
through several towns, and the system of improvement 
by small districts works injustice both ways — upon 
those who are obliged to keep a road for the use of 
others and upon those who are obliged to use a road 
they cannot cause to be kept in proper condition. 

County management seems more successful in this 
country than any other, as a county, or two counties 
combined if necessary, is usually strong enough to 
secure intelligent management and homogeneous 
enough to have common interests. 

The proper management of the common roads in 
any community requires both experience and intelli- 
gence. A man to be efficient in such work must be 
able to make or modify location where necessary, 
judge of the value of various materials for purposes of 
construction, determine the necessity for and means to 
be adopted for drainage, and possess the executive 
ability to manage men and control scattered work. 
The work in each locality is a problem by itself, to be 
solved by careful study of the requirements of the 
community, taking into account the local natural 
conditions and available materials and means. 

Several of the states have State Highway Commis- 
sions, or State Highway Engineers, for the purpose of 
promoting the improvement of the country roads. 



ROAD ECONOMICS AND MANAGEMENT. 2$ 

These commissions are usually mainly advisory in 
character. They investigate and report upon the 
condition and needs of the roads, advise the local 
authorities concerning the best methods of construction, 
furnishing plans and specifications if desired, and 
control the expenditure of state funds applied to road 
purposes. These commissions have accomplished much 
in the way of improving existing conditions in several 
states, and have done much toward creating sentiment 
favorable to the expenditure of funds for such work. 
In Missouri the new road law provides a combined 
county and district management. It creates the office 
of County Road Engineer to be appointed by the 
county court. The County Engineer has direct charge 
of the expenditure of the general county road and bridge 
fund, and all district road supervisors in the county 
are required to report to him and to conduct their work 
under his general direction. The purpose is to provide 
a competent central authority in each county, without 
changing the existing division into road districts. 
There is also a State Highway Engineer whose duties 
are to advise with the local authorities, and to dis- 
tribute and control the expenditure of state appro- 
priations in aid of road improvement. 



CHAPTER II. 

DRAINAGE OF ROADS AND STREETS. 
Art. 9. Necessity for Drainage. 

The road-bed, usually formed of the natural earth 
over which the road or pavement is to be constructed, 
must always carry the loads which come upon the 
road surface. Where an artificial road surface or 
pavement is employed, the earth road-bed is protected 
from the wear of the traffic, and the wheel loads com- 
ing upon the surface are distributed over a greater 
area of the road-bed than if the loads come directly 
upon the earth itself; but the loads are transferred 
through the pavement to the road-bed, and not sus- 
tained by the pavement as a rigid structure. 

The ability of earth to sustain a load depends in a 
large measure upon the amount of moisture contained 
by it. Most earths form a good firm foundation so 
long as they are kept dry, but when wet they lose 
their sustaining power, becoming soft and incoherent. 
When softened by moisture the soil may be easily 
displaced by the settling of the foundation of the 
road, or forced upward into any interstices that may 
exist in its superstructure. 

In cold climates the drainage of a road is also impor- 
tant because of the danger of injury from freezing. 
Frost has no disturbing effect upon dry material, and 
hence is an element of danger only in a road that 
retains water. 

26 



DRAINAGE OF ROADS AND STREETS. 2*J 

In order, therefore, that the loads may be uniformly 
sustained, and the surface of the road kept firm and 
even, it is evidently of first importance that the road- 
bed be maintained in a dry condition. The improve- 
ment and maintenance of a road are therefore largely 
questions of drainage, the object being to prevent water 
from reaching the road and to provide means for 
immediately removing such as does reach it before the 
soil becomes saturated and softened. 

Surface drainage is always necessary if the body of 
the road is to be kept in a dry condition, and is accom- 
plished by having the surface of such form that water 
falling upon it will quickly run into the gutters. 

The necessity for underdrainage in any case depends 
upon local conditions, the nature of the soil and the 
tendency of the site to dampness. Underdrains are for 
the purpose of lowering the level of ground water in wet 
weather and preventing water from underground 
sources reaching the road bed and softening it. A 
careful examination of local conditions is necessary 
in any case to determine the advisability of constructing 
underdrains. Where the soil upon which the road is 
constructed is so placed that the ground water is at 
any time likely to stand close to the surface and become 
soft immediately under the road-bed, underdrainage 
is necessary to good results in the maintenance of the 
road. In any case in which the level of ground water 
stands within about 3 feet of the surface, the road will 
be benefited by sub-surface drainage, although it may 
not be altogether necessary to the maintenance of the 
road. Underdrainage is of little use for the removal 
of water from depressions in the surface of the road. 



28 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. io. Surface Drainage. 

The drainage of the surface of a road is provided for 
by making the section higher in the middle than at the 
sides, with ditches or gutters at the edges of the road 
along which the water is conducted until it may be dis- 
posed of through some side channel. 

The slope necessary from the middle to the sides of 
the road to insure good drainage depends upon the 
nature of the road surface, being less as the road surface 
is more smooth and less permeable to water. For 
ordinary earth roads it varies from about I in io to 
I in 20; for macadam or gravel roads, from 1 in 15 
to I in 30; and for brick or asphalt pavements, from I 
in 40 to I in 60. 

The drainage of the surface of a country road is 
mainly a matter of maintenance, and involves keeping 
the surface of the road in a smooth condition and 
properly crowned. It is more fully discussed in Arts. 
25 and 27. 

On country roads the disposal of surface water is not 
usually a matter of difficulty, as it can be carried along 
the road and run into the first convenient cross channel. 
In deep cuts or on steep grades, however, it may some- 
times be economical to lay a pipe under the gutter 
into which surface water may be turned at frequent 
intervals. 

In all cases it is important that the water which 
falls upon the surface should be gotten rid of as soon 
as possible, for»so long as it remains upon the road it 
is an element of danger, both from its tendency to 
wash the surface, and from its liability to penetrate 
into the road and thus cause disintegration or settle- 
ment. 



DRAINAGE OF ROADS AND STREETS. 29 

ART. II. SUBDRAINAGE. 

The drainage of the subsoil under a road is intended to 
lower the level of ground water in wet weather and 
prevent water from sub-surface sources reaching the 
road-bed. 

The necessity for subdrainage, and the method to 
be employed in any case, depends upon whether the 
soil over which the road is being constructed is natu- 
rally wet or dry, and whether the road-bed is so situ- 
ated and formed as to give it natural drainage. 

The material of which a road-bed is composed is 
important because it determines to a large extent 
whether artificial drainage is necessary, and also what 
method should be adopted for securing drainage. 

Soils differ in their power to resist the percolation 
of water through them, in the rapidity and extent of 
their absorption of water with which they come in con- 
tact, in the extent to which moisture renders them soft 
and unstable, and in their power of retaining moisture. 

A light soil of a sandy nature usually presents little 
difficulty in the matter of drainage, as, while it is easily 
penetrated by water, it is not retentive of moisture, 
which passes freely through it without saturating it 
unless prevented from escaping. 

If the natural drainage, therefore, have a fall away 
from a road-bed formed of such material, it will usually 
need no artificial drainage, and where subdrains are nec- 
essary they may be relied upon to draw the water from 
the soil to a considerble distance each side of the drain. 

A nearly pure sand is more firm and stable, under 
loads, when quite damp than if dry, although a fine 
sand saturated by water which is unable to escape 
may become unstable and treacherous. 



30 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Clays usually offer considerable resistance to the 
passing of water through them, and are very retentive 
of moisture. As a rule, however, a clay soil does not 
absorb water readily, and requires that water be held 
for some time in contact with it in order that it may 
become saturated, although when saturated it is the 
most unstable of soils. A clay that when dry will 
stand in a vertical wall and support a heavy weight, 
when wet may lose all coherence and become a fluid 
mass. When water comes in contact with a bed of 
such clay, the outside becomes saturated and semi- 
fluid before the moisture penetrates into it sufficiently 
to even moisten it a few inches from the surface. 

A clay soil is, therefore, always difficult to drain by 
removing the water after it has soaked in, or by per- 
mitting it to pass through the road-bed to the subdrains 
beneath. Drainage, in such cases, may often be so 
arranged as to prevent water from standing against 
the road and thus prevent it from becoming saturated. 
As the clay is comparatively non-absorptive, the water 
which may come upon its surface, if allowed to escape 
at once, will not penetrate into it, and hence will not 
cause softening. 

A heavy silt formation is sometimes met with which 
is even more difficult to drain than a true clay. It is 
nearly as retentive of moisture as a clay, strongly 
resisting the passage of water through it, but at the 
same time absorbs water quite freely when in contact 
with it. 

Between the extremes mentioned above there are 
a great number of varieties of soil which possess to a 
greater or less extent the characteristics of either or 
both, and gradually merge the one into the other. In 
applying a system of drainage in any case, careful 



DRAINAGE OF ROADS AND STREETS. 3 1 

attention should always be given to the characteristics 
of the soil, as determining very largely the treatment 
to be used. 

Where artificial sub drainage is necessary the drains 
should be located, in so far as possible, with a view to 
cutting off the supply of water before it reaches the 
road-bed. To accomplish this to the best advantage 
the local conditions must be observed, the sources of 
this supply determined, and the nature of the under- 
flow, if any exist, considered. In most instances on 
roads over soil commonly met upon country roads a 
single line of tile under one side of the road will lower 
the ground water sufficiently to prevent it reaching 
the road-bed. 

Frequently, as in many cases of a road along a side 
slope, there is a well-defined flow of sub-surface water 
from one side to the other, and in such case the water 
may perhaps be intercepted by a single longitudinal 
drain on the side of the roadway from which the 
water comes. An example of this is shown in Fig. 3. 



V hlMWHI>J. W*l \\\\\\\' 



Fig. 3. 

When the subsoil is of stiff and retentive material 
which does not drain readily, an underdrain on one side 
may not draw the water from under the whole width 
of the roadway. In this case it is advisable to use a 
drain on each side to cut off the water before it reaches 
the roadway. This may be necessary with a clay soil 
when the line of ground water is high. 

Sometimes a single drain is laid under the middle of 




32 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the road, as shown in Fig. 4. This is, in general, an 
undesirable practice; the middle of the roadway is 
not a convenient place for the drain, and necessitates 
digging a trench under the roadway which is likely 
to give considerable trouble in the early maintenance 
of the road surface. In some instances however a 
spring of water may come up under the roadway, as in 
a clay spout, and when this occurs it is desirable to lay 
a pipe to take the water from the source of supply 
rather than to drain it through the soil to the side 
drains. 

The most satisfactory and cheapest method of under- 




Fig. 4. 



drainage is commonly by the use of porous drain tile, 
as used for farm drainage. Where stone is plentiful 
and handy to the road, a stone drain may be. cheap and 
equally effective with the tile. These types of drains 
are described in succeeding articles. 

Many road builders utilize the side ditches, intended 
for surface drainage, for underdrainage also by making 
them deep and narrow. This is not usually an eco- 
nomical practice. A tile drain and shallow gutters 
will not be more expensive to construct than the deep 
ditches, while they are much easier and cheaper to 
maintain. In some instances tiles are laid under the 
surface ditches and the trenches filled with stones, or 
gravel, as shown in Fig. 5, thus permitting the surface 
drainage to seep into the tile. This gives very effective 



DRAINAGE OF ROADS AND STREETS. 33 

drainage, if the tile be of sufficient capacity, but is 
expensive to construct. 

In considering the advisability of underdrainage and 
the method of accomplishing it, the fact should be 
kept in mind that the purpose of underdrainage is to 
remove ground water, and that efficient drainage of 




Fig. 5. 

the road surface can only be accomplished by main- 
taining the surface in smooth condition and of proper 
form. 

Art. 12. Tile Drains. 

Tile drains for road drainage are constructed in the 
same manner as for land drainage. Ordinary porous 
tiles are used as in farm drainage, sizes from 4 to 8 or 
10 inches in diameter being commonly employed for 
this purpose. They are usually in lengths of slightly 
more than 12 inches, the excess of length being sufficient 
to allow for probable breakage, so that estimates may 
be made on the basis of one tile to each foot of length. 
The tiles should be truly cylindrical with the ends cut 
off square, and be smooth inside. They are laid in a 
trench 3 or 4 feet below the surface of the ground, with 
their ends in contact. They should be carefully placed 
so that the ends fit closely, and the bottom of the 
trench should be cut to about the width of the tile, so 
that they cannot move sideways when the trench is 



34 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

filled; or better still, a groove may be scooped out in 
the bottom of the trench to fit the tile. 

Grade of Tile. The velocity of water through a tile 
depends upon the slope of the tile. Considerable water 
may be carried by a tile laid to an almost level grade. 
Such grades are, however, rarely necessary in road 
drainage and are to be avoided whenever possible. It 
is not desirable, except under unusual conditions, to 
use a grade less than about 2 inches per 1 00 feet. This 
gives a velocity which may be reasonably expected to 
keep the tile clear, when properly laid, except for small 
tiles, although a greater slope is to be preferred when 
obtainable. 

Care should be used in laying tile to place it accu- 
rately to the grade line, particularly when the slope is 
light. Irregularities are apt to produce depressions in 
which deposit of silt may take place. 

Size of Tile. A tile for road drainage should not be 
less than 4 inches in diameter. While a smaller tile 
may often be large enough to carry the water, the 
danger of clogging is much greater and the effect of 
inequalities in grade are increased for such tile. The 
size of tile required depends upon the quantity of water 
to be carried and the slope of the tile. For agricultural 
drainage it is common to assume that the tile must 
remove from J inch to 1 inch of water per day over the 
area which it drains. The rules commonly followed 
probably give an excessive run-off in most instances, 
and recent observations indicate that \ inch would be 
ample in most instances of ordinary drainage. This 
method may be applied in road work where the area 
from which the water is drawn can be determined. 
The area to be included depends upon the character 
of the soil and the way the ground lies. On level 



DRAINAGE OF ROADS AND STREETS. 35 

ground the drain may be assumed to receive water 
from a certain distance on each side depending upon 
the porosity of the soil. 

For road drainage the size of tile used should be 
such as to provide liberal capacity. Comparatively 
small sizes will usually be required and the differ- 
ences in cost are small. An area of 25 to 50 feet on 
each side may be considered as contributing water 
to the tile. In ordinary soil the effect of the tile will 
reach much farther than this, but the percolation is 
so slow that the water will reach the tile very 
gradually. 

This method may serve as a guide in selecting the 
size of tile required, but is not capable of accurate 
computation and is only of value as an aid to judg- 
ment. Good practice in such work must rest mainly 
upon the judgment derived from experience. If the 
tile be supposed to collect water from about 25 feet 
on each side, it would drain about an acre for each 
870 feet of length, or about 6 acres per mile. Assum- 
ing one-half inch in 24 hours, over the drainage area, 
as the amount to be provided for, one acre will yield 
1 81 5 cubic feet per day, or i| cubic feet per minute; 
and one mile of length, 50 feet wide, will yield about 
7^ cubic feet per minute. 

The water carrying capacity of tile drains has not 
been accurately determined but it probably does not 
greatly differ from that for vitrified pipe sewers, and 
the use of the formulas usually applied to sewers will 
be sufficiently accurate for practical purposes. The 

common formula for the flow of water, v = C VRS, may 

for our purpose be transposed into the form V = k \DS, 
in which V is the velocity in cubic feet per second, 
D is the diameter of the pipe in inches, S is the slope, 



36 



A TEXT-BOOK ON ROADS AND PAVEMENTS. 



and k is a coefficient varying from about 9 for 4-inch 
pipe to 12 for 12-inch pipe. 

The following table for the capacity of tile drains is 
based upon this formula. It is computed by the use 
of Kutter's formula, using a coefficient of roughness 
of .013, which corresponds to the flow in pipe sewers. 



CAPACITY OP 


TILE DRAINS IN 


CUBIC FEET PER 


MINUTE 


Slope per ioo 












Feet. 






>izes of Pipe 






In. 


Feet. 


4 In. 


6 In. 


8 In. 


10 In. 


1 2 In. 


2 


.67 


4- 


12 . 


27. 


49-5 


81 . 


4 




•33 


5-5 


16.5 


38. 


70 




114 




6 




■5° 


6-5 


21 . 


46.5 


86 


5 


143 




9 




•75 


8. 


25-5 


57-5 


106 


5 


176 




12 




1 . 


9-5 


29-5 


66. 


122 


5 


204 




24 




2 . 


13-5 


4i.5 


92.5 


173 




288 




3* 




3- 


16.5 


5i- 


114. 


212 




353 




48 




4- 


19. 


59- 


132. 


245 




408 




60 




5- 


21 . 


66. 


148. 


275 




45 6 





Tiles laid upon very flat slopes sometimes may carry 
a quantity of water greater than the capacity due to 
the slope; this is caused by the level of ground water 
standing above the tile, thus causing the water to 
flow in the tile under a head greater than that due 
to its slope. Where gravel or other porous material 
is available such tile will be benefited by a porous 
filling immediately over the tile. This also assists in 
keeping the tile clear of sediment. 



Art. 13. Stone Drains. 

In localities where stone suitable for such purposes 
exists along a roadway it is common and often econ- 
omical to use stone drains for purposes of under- 
drainage. 



DRAINAGE OF ROADS AND STREETS. 



37 



Blind Drains. For short lengths, where it is only 
necessary to provide a permeable path for a small 
quantity of water to escape, blind drains may be used. 
They consist of ditches cut into the soil and filled at 
bottom with fragments of stone, the trench then 
filled with earth. Care should be taken that the top 
of the stone is protected, so that the earth may not 
be washed into the stone and stop the drain; a little 
small-sized stone or gravel on top, or a light layer of 
brush or sod, to hold the earth until it has compacted, 
is useful. Such drains have frequently proven quite 
efficient when used where the requirements are not too 
great. 

Box Drains. Where suitable stone is plenty and 
cheap, a box drain" may be built. This consists of a 





Fig. 6. 



Fig. 7. 



rectangular box formed of flat stones at the bottom of 
the trench, which is then filled with earth. This box 
may be very roughly built, and it is desirable when 
stone or gravel is plentiful to fill immediately over 
the drain with such material, to protect it against the 
entrance of earth and assist in leading the water into 
it. Figure 6 shows a section of such a drain as con- 



38 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

structed to intercept a seepage of water in stiff reten- 
tive material. In ordinary soil there would be no 
advantage in filling the trench so full of stone. The 
construction shown in Fig. 7 is also sometimes used, 
and is cheap and reasonably efficient. 

The size of opening in a stone drain must be consid- 
erably larger than that in a tile to carry the same 
quantity of water, the construction usually being very 
rough, and the resistance to flow greater. Drains of 
this type are used in many localities where materials 
are available for building them, although their use is 
growing less, due to the fact that porous tile costs so 
little and tile drains are so easily and cheaply con- 
structed. 

Art. 14. Culverts. 

Culverts are commonly required in road construction 
for carrying under the road the small streams which 
may be crossed by the road, or sometimes for carry- 
ing the water collected in the gutters or ditches on 
the upper side of the road to the lower side. 

The waterway provided by a culvert must, for 
safety, be sufficiently large to pass the maximum flow 
of water that is likely to occur, while for economy it 
must be made as small as may be without danger. 

The maximum flow of a stream depends upon a 
number of local conditions, most of which are very 
difficult of accurate determination. These are: the 
maximum rate of rainfall, the area drained by the 
stream and its position, the character of the surface 
drained, and the nature of the channel. 

The. maximum rate of rainfall varies in different 
localities, and differs in the same locality from year to 
year. It is commonly taken at about an inch an hour. 



DRAINAGE OF ROADS AND STREETS. 39 

This is sometimes exceeded for a very short time and 
over a small area, but is usually a safe value for a 
watershed of any considerable area. 

The approximate area of the watershed drained by 
a stream is readily found, and its form is also impor- 
tant as determining the distance the water must flow in 
reaching the culvert under consideration, and to some 
extent regulating the rate at which the water falling 
upon the area will reach the culvert. 

The maximum flow of a stream is also affected by 
the physical characteristics of the watershed. The 
permeability of the surface largely determines what 
portion of the rainfall shall reach the stream; while the 
slope of the surface, its evenness, and its vegetation 
have an effect upon the quickness and rate with which 
the rainfall is received by the stream. 

The determination of the maximum flow to be ex- 
pected in any case from an examination of the locality 
is therefore possible only as a very rough approxima- 
tion. A number of formulae have been proposed for 
such estimation, the use of which for the case of an 
ordinary culvert simply amounts to estimating the 
quantity of water which would fall on the watershed in 
the heaviest probable rain, and judging as well as pos- 
sible from local conditions how much of it may arrive 
at one time at the culvert. In some cases where a 
more accurate determination is desirable it may be 
advisable to measure the flow of the stream at high 
water, and form an idea from such measurement as to 
what may be expected at a maximum stage. 

The amount of water that will pass a culvert in. a 
given time depends upon the form of the section, the 
smoothness of its interior surface, its slope, and the 
head under which the water is forced through. A 



40 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

well-constructed culvert may be considered in comput- 
ing its capacity as a pipe flowing full. Other culverts 
or bridges must be treated as open channels. 

Prof. Talbot gives (Selected Papers C. E. Club, Univ. 
of Illinois, 1887-8) a formula for the rough determina- 
tion of area required for waterway, derived from ex- 
perience : 

Area waterway in feet = C V (drainage area in acres) . 3 
C is a coefficient depending upon local conditions. 
For rolling agricultural country subject to floods at 
time of melting snow, and with length of valley 3 or 4 
times the width, C = J. When the valley is longer, 
decrease C. If not affected by snow and with greater 
lengths, C may be taken at J, £, or even less. For 
steep side slopes C should be increased. 

For most cases in practice the size of waterway 
required may be determined from the knowledge which 
usually exists in the vicinity regarding the character of 
a stream, from the sizes of other openings upon the 
same stream, or from comparison with other streams 
of like character and extent in the same locality. 
Where data of this kind do not exist, careful exami- 
nation of water-marks on rocks, the presence of drift, 
etc., may be made to determine the height to which 
water has previously risen. The shape of the valley 
and the slope of the surface is of more importance 
than the area of country drained. The use of a for- 
mula like Talbot's assists the arrangement of the 
factors which enter into the determination, and is 
only intended as an aid to judgment in selecting the 
size of opening required. 

The discharging capacity of a culvert will depend 
upon the slope of the water surface passing through 
the culvert. Increasing the slope of the bed of the 



DRAINAGE OF ROADS AND STREETS. 4 1 

culvert will increase its carrying capacity, provided 
the water can flow freely away below the culvert. If 
a culvert be so constructed as to permit the water 
to dam up above it, causing the culvert to flow full and 
under pressure, the effect is the same as increasing the 
slope and increases the capacity of the culvert. The 
velocity through a culvert is approximately propor- 
tional to the square root of the head of water, the 
head being the difference of elevation of the water 
surface at the entrance to the culvert and that where 
the water leaves the culvert. 

There are three types of culverts in common use for 
road purposes: stone box culverts, pipe culverts, and 
concrete culverts. In some localities wooden box cul- 
verts are also used for this purpose; these are very un- 
economical on account of their perishable nature and 
their use should be abandoned. 

Stone Culverts. Culverts of stone may be either 
arch culverts or box culverts. Box culverts are usually 
formed of two side walls and a cover. The side walls 
consist usually of rubble stonework laid up dry or in 
mortar, as the case may be. Where the stream to be 
carried is of small importance, and the capacity of the 
culvert not greatly taxed, dry walls may give satis- 
factory results, but when the culvert is likely to flow 
full at certain times it should be laid up in hydraulic 
cement mortar, and in any case the greater stability 
given by the mortar would be well worth the small 
additional cost. Fig. 8 shows a section of the ordi- 
nary form of box culvert. The use of head walls and 
paving the waterway for a short distance is necessary 
for these, as for pipe culverts. 

Where suitable stone is available, box culverts are 
easily constructed and economical. They are com- 



42 



A TEXT-BOOK ON ROADS AND PAVEMENTS. 



monly used for openings 2 to 4 feet in width and 
2 to 5 feet in height. The width that may be used 
depends upon the available cover stones. Where the 
allowable width is not sufficient to give the needed 
area of waterway, a double culvert may sometimes be 
used to advantage. This consists of two openings 
with a middle wall to support the covers. 

The culvert's opening should always be large enough 
to admit of a man passing through it for the purpose 




Fig. 8. 

of cleaning it — at least 18 by 24 inches. The side walls 
should extend downward below the bottom of the 
culvert sufficiently to obtain a good foundation, and 
the thickness required for the side walls usually varies 
from one-half to three-fourths the height, depending 
upon the pressure likely to come against them. 

In many cases for small work the side walls, instead 
of extending downward, rest upon the paving which is 
extended under them. This gives a somewhat less 
expensive construction, and is often satisfactory on 
good ground. 

The cover stones may be from J to § the span in 
thickness, and should be long enough to have a bear- 



DRAINAGE OF ROADS AND STREETS. 43 

ing upon each side wall of at least one-half the thick- 
ness of the wall. 

Pipe Culverts. Pipe culverts may be constructed 
either of salt-glazed vitrified sewer pipe, or of iron 
water pipe. For culverts of sizes up to about 30 inches 
diameter, vitrified pipe is often the most economical 
material to use provided it is placed on good founda- 
tion and sufficiently covered not to be subject to shock 
from the traffic. The iron pipe possesses greater 
strength, and is preferable where a firm foundation is 
not easily obtained, or where a sufficient covering can 
not be had for the vitrified pipe, as it is not so easily 
broken by a slight settlement or by shocks. It is 
somewhat expensive and not economical for ordinary 
use. 

In laying pipe culverts, they should be placed on a 
solid bed, and the earth be well tamped about them. 
It is desirable to have the bottom of the trench exca- 
vated to fit the lower part of the pipe, depressions 
being formed for the sockets. It is necessary in every 
case that the pipe be firmly and uniformly supported 
from below, in order that the culvert may not be 
broken by settlement, which is especially likely to 
occur in new work. 

The joints in the pipe should be made water-tight, 
especially where the culvert is likely to flow full or 
under pressure, as any water escaping through the 
joints will tend to cause a wash beneath the pipe and 
undermine the culvert. Joints are commonly filled 
with clay, but where strength is needed the use of 
hydraulic cement mortar is preferable. The cost of 
filling joints is small and adds much to the security 
of the culvert. 

Care should be taken that the culvert have sufficient 



44 



A TEXT-BOOK ON ROADS AND PAVEMENTS. 



slope and be so placed that water may not stand in 
it, in order to prevent injury from freezing. When this 
is not feasible, iron pipe should be used. The top of 
the culvert pipe should be at least 1 8 inches below the 
road surface to avoid crushing, and for the larger sizes 
of pipe (24 to 36 inches), at least two feet. 

The ends of pipe culverts should be set in masonry 
walls to give protection against the washing of the 
face of the embankment, hold the ends firmly in place, 
and prevent the entrance of water into the earth on 
the outside of the pipe. 

These walls to give efficient protection must be of 
substantial construction, going down to a solid founda- 
tion below the bed of the stream. They may be built 
of rubble masonry, and should be laid up in hydraulic 
cement mortar. Such construction is represented in 
Fig. 9. The wall must extend far enough on the side 




lumim.mmum m 



] ' 




.umiumummuum 




Fig. 9. 



to sustain the earth of the embankment from the 
waterway, or wing walls may be used extending up 
stream for this purpose. The waterway should be 
paved above the culvert far enough to prevent scour- 
ing at the base of the wall. 



DRAINAGE OF ROADS AND STREETS. 45 

For quite small streams the walls may sometimes 
be omitted if the face of the embankment about the 
entrance to the pipe and the waterway for some dis- 
tance above and below be riprapped. Where it is 
necessary to economize in the cost of construction, 
this method is preferable to the use of very light end 
walls. 

On streams too large for a single pipe it is often 
economical to lay two or three pipes side by side, 
rather than to construct an arch or the open way of a 
bridge. In laying large pipes it is usually advisable 
to place a broken-stone or concrete foundation under 
the pipes throughout their lengths to insure uniform 
support. 

Art. 15. Concrete Culverts. 

Where the waterway required is too large to permit 
the use of vitrified pipe, concrete culverts are, in most 
instances, the most economical to use, and in many 
locations they may be placed more cheaply than the 
larger sizes of pipe culverts. Concrete, made of good 
materials, and properly mixed and placed, is a very 
durable material and will last indefinitely. A well 
designed concrete culvert should therefore require very 
little in the way of maintenance. 

These culverts are built either with arched or flat 
tops. For small spans, the rectangular box form is 
usually the most economical. The arched culvert for 
small spans is usually built of solid concrete without 
reinforcement, and is heavier than the box form, unless 
the culvert be very small. For longer spans the rein- 
forced arch is desirable. 

Fig. 10 shows the section of a concrete culvert in 
which the sides and bottom, as well as the top, are 



46 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



reinforced with steel rods, for the purpose of taking 
the tension due to the tendency to bend under the loads 
which come upon it. Concrete is a good material for 
resistance to compression, but offers slight resistance 
to tension; the introduction of steel rods to take the 
tensions, therefore, make it possible to construct the 
walls and top of the culvert much lighter than they 
could otherwise be built. 

Structures of this kind must be carefully designed 
and constructed in order to secure good results. The 
steel should consist of small rods well bedded in the 
concrete. They should be placed with the center of 

the rods about two 
inches from the inner 
surface of the concrete. 
The area of steel re- 
quired in the top of 
such a culvert is usu- 
ally about one per 
cent of the area of the 
concrete above it. 

Concrete culverts, 
like pipe culverts, must 
be protected by a covering of earth from the shocks 
of the traffic. This covering should be 1 8 inches in 
thickness, and in no case should be less than 12 inches. 
The ends of the culvert must be protected by walls, 
which should extend at least two feet below the bottom 
of the culvert. 

The thickness of the top and sides must depend upon 
the loads which may come upon the culvert and upon 
the character of the concrete. They should usually 
be designed to safely carry a heavy road roller. The 
concrete should be made of the best grade of Portland 




Fig. 10 



DRAINAGE OF ROADS AND STREETS. 



47 



cement mixed with good quality sand and gravel, or 
broken stone, so as to produce a very dense, homo- 
geneous concrete, the proportions for the top being 
about I part cement, 2 parts sand, 4 parts broken 
stone; for the sides and bottom, 1 part cement, 2 \ 
parts sand, 5 parts broken stone or I part cement, 3 
parts sand, 6 parts broken stone. The following tables 
give approximate dimensions for culverts suitable for 
country roads under these conditions: 



TOP OF CULVERT. 












Span in feet 


3 

8 

I 
6 

3 

5 
5 

8 
l8 

2 

6 

1 

12 


4 

9 
3 

8 

4 
6 
1 

12 

3 
6 

\ 

10 


5 
10 

I 

7 

5 
7 
\ 

10 

4 
7 
f 

12 


6 
11 
I 

6 

6 
8 
f 

16 

5 
8 
5 

8 
IO 


8 


Thickness of concrete, — inches. . 
Size of steel bars, — inches square 
Distance apart of bars, c. to c. — 

BOTTOM OF CULVERT. 
Span in feet 


13 
I 

6 

8 


Thickness of concrete, — inches. . . 
Size of steel bars, — inches square . 
Distance apart of bars, c. to c. — 

SIDES OF CULVERT. 

Height of opening, — feet 

Thickness of concrete, — inches. 
Size of steel bars, — inches square . 
Distance apart of bars, c. to c. — 


9 

i 

12 

6 
9 
\ 

12 







It may sometimes be desirable to leave out the con- 
crete bottom, and extend the side walls deeper, as with 
a stone box culvert. Where this is done, the side walls 
should extend at least 18 inches below the bottom of 
the culvert, and should widen at the bottom into a 
footing which will give a firm foundation to the 
structure. 



48 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

For small culverts on country roads the side walls 
may be of plain concrete, with a thickness of about 
one-third of the height. For the smaller sizes this 
may in many instances be cheaper than the reinforced 
sides. For openings not more than 1 8 inches to 2 feet 
square a semicircular arched opening, without rein- 
forcement, with a thickness of arch and side wall of 
about one-third the diameter, may be cheaper than the 
rectangular form of opening. 

In work of this kind, great care must be taken to 
secure good materials; the broken stone should be of 
good hard material, not too uniform in size, varying 
from about f-inch to I \ or I J inches; sand should 
preferably be coarse and not uniform in size, it should 
be clean, hard sand; cement should meet the specifi- 
cations of the American Society for Testing Materials 
for Portland cement. The mixing and placing of the 
concrete must be carefully done so as to secure a 
thorough and uniform mixture of the ingredients, and 
a dense, compact mass of concrete in the culvert. 



CHAPTER III. 
LOCATION OF COUNTRY ROADS. 

Art. i 6. Considerations Governing Location. 

The determination of a line for a proposed road 
involves the examination of the country through which 
the road is to pass with reference to its topographical 
features, the nature and extent of the traffic that it 
may develop, and the local interests that may be 
affected by the position of the road. 

The simplest form that this problem can take is that 
in which two points, as two towns, are to be connected 
by a road for the purpose of providing for a traffic 
between them, the nature and amount of which is 
approximately known. In this case it is only necessary 
to examine the topography of the intervening country 
and select the line over which, taking into account 
the costs of construction and maintenance, the given 
traffic may be most economically carried. 

In most cases in practice, however, the problem 
does not have this simple character, and in fact location 
can seldom be determined by considerations of economy 
alone. The position of the line will be modified by 
local needs, such as the necessity of providing for the 
traffic of villages or farms intermediate between the 
ends of the road, which may often cause deviations 
from what would be the best line if the interests of 
the terminal points alone were considered. 

Questions of the desirability of various lines for the 
comfort and convenience of travel, and the pleasure to 

49 



50 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

be derived from the use of the road, dependent upon 
aesthetic considerations, may also frequently operate 
to change the line from what would seem proper from 
a strictly economic point of view. 

In thickly settled communities, as in most parts of the 
United States, the roads are in the main already located, 
the necessity for the location of new ones does not often 
arise, and when it does occur is usually mainly deter- 
mined by the local needs and requirements of traffic. 

The economic considerations involved in the location 
of roads are of two kinds: those relating to the accom- 
modation of traffic, and those relating to its economic 
conduct. The first deals with the necessity of the road 
to the community, the second with the cost of operat- 
ing it. The first involves the general question of the 
advisability of any road, and how it can be placed to 
give the greatest freedom to the movement of travel. 
The question is as to the value of the road to the gen- 
eral community and its location to secure the greatest 
good for the least outlay, without taking into account 
the details of location which may affect the cost of 
transportation. The value of the road as developing 
trade in a town or bringing a farm nearer to market 
would enter into consideration. The accommodation 
of traffic requires that a road be located with a view to 
the convenience of its use by the largest portion of the 
traffic, as well as with a view of developing traffic. 

The position of a road that will best accommodate 
traffic is that in which, other things being equal, the 
mass of traffic need be moved the least distance in 
reaching its destination; or, in other words, that for 
which if each ton of freight be multiplied by the dis- 
tance through which it must be moved the summation 
of the resulting products will be a minimum. If there 



LOCATION OF COUNTRY ROADS. 5 1 

be differences in the nature of the routes over which 
the road may be constructed, they may be considered 
as equivalent to changes in the relative effective lengths 
of line for purposes of comparison. 

The ordinary problem of location deals mainly with 
considerations of the second class. It consists for the 
most part in the relocation of portions of old roads, 
of making such changes in position when improving a 
road as may tend to reduce the cost of conducting 
traffic over it and render it more convenient and 
pleasant for the use of travel, or of determining the 
details of alignment and grade upon a new road which 
is approximately fixed in position by the purpose of 
its construction. 

The most economical location is that for which the 
sum of the annual costs of transportation, the annual 
costs for maintenance, and the interest on the cost of 
construction is a minimum. 

The cost of conducting transportation is affected by 
the rate of grade of the road, the amount of rise and 
fall in it, and the length of the road. The rate of 
grade is important, because it limits the loads that can 
be hauled over the road, or determines the number of 
loads that must be made to transport a given weight 
of freight, as well as fixes a limit to the speed of travel. 
The amount of rise and fall affects the expenditure of 
power required to haul a load over the road. The 
length of the road has an effect upon the amount of 
work necessary to haul a load over it, the time required 
for a trip, and the cost of maintaining the road surface; 
each of which, other conditions being the same, is 
directly proportional to the length. 

The cost of construction depends upon the accuracy 
with which the line of the road is fitted to the surface 



52 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of the ground, as determining the amount of earth- 
work and cost of bridges and culverts; upon the 
character of the ground over which the road is to be 
built, which affects the cost of executing the work and 
determines the necessity for and expense of drainage; 
and upon the cost of land for right of way. All of these 
items must be considered in any comparison of the 
cost of constructing on various routes. Special care 
should be taken in selecting a line to avoid bad ground, 
such as swamps, upon which construction may be diffi- 
cult and expensive. The availability near the line of 
the road of materials needed for surfacing may also 
become a matter of importance in the cost of construc- 
tion, and have an influence in determining location. 

The relative importance of the various elements 
affecting the choice of a line depends upon the nature 
and amount of the traffic to be provided for and upon 
the character of the road surface to be used. Where 
the traffic is heavy, the importance of reducing the 
cost of moving it by lessening grades and distance will 
be greater than where the traffic is light, and the cost 
of construction may be correspondingly increased for 
that purpose. If a smooth surface be employed, upon 
which traction is light, the value of reducing grades 
will be greater and the value of reducing distance less 
than with a surface of poorer tractive qualities. 

Art. 17. Length of Road. 

Changes in the length of a road affect all portions of 
the traffic in the same manner, and the expenditure of 
power and loss or gain in time occasioned by them are 
in general directly proportional to their amounts. 

The value of any considerable saving in length may 
usually be considered as equal to the same percentage 



LOCATION OF COUNTRY ROADS. 53 

of the whole cost of conducting the traffic that the 
saving in distance is of the whole length. If, therefore, 
a rough estimate may be made of the annual traffic to 
be expected upon a given line of road and of the cost 
of carrying the traffic, this cost divided by the length 
in miles through which the traffic is moved will give 
the annual interest upon the sum that may reasonably 
be expended in shortening the road one mile, or upon 
the value of a saving of a mile in distance; or dividing 
by the number of feet of distance will give the value of 
saving one foot. 

It is to be noted, however, that the cost of the work 
of transportation is not necessarily proportional to the 
amount of work done, and consequently this method 
would not be strictly accurate even were the data as 
to traffic and costs readily obtainable. An estimate of 
this character at best amounts to only a rough guess, 
but it may often be of use as an aid to the judgment 
in deciding upon the value of a proposed improvement 
involving a considerable change of length in a road. 

Where the road is so situated and the saving in 
distance proposed is such that it would enable teams 
to make an additional trip per day in the hauling of 
freight, the difference in cost of transportation is quite 
tangible and readily estimated; but where the traffic is 
of a more indefinite nature, or the saving proposed 
insufficient to admit of additional trips, the value of 
the difference of length depends upon the value to 
other work of the small portions of time of men and 
teams which may be saved by the shorter route — a 
value which exists, but is difficult to estimate. 

There is also a value in the saving of distance due 
to the advantage to the community of bringing the 
various points closer together, such as bringing two 



54 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

towns into closer relations or bringing country property- 
nearer to markets. The method of considering the 
cost as proportional to the work done will therefore 
probably give a fair idea of the actual economy in any 
saving in the work of transportation. 

The value of reducing distance varies with the 
character of the road surface. As the cost of transpor- 
tation is less over a smooth than over a rough surface, 
on account of the lighter traction, the value of reduc- 
ing distance is also less on the smooth surface. 

The value of saving distance also is greater on a 
road where the ruling gradients are steep than upon 
one with light gradients, because of the greater num- 
ber of loads necessary to move the same traffic. 

The cost of maintenance of a road varies with its 
length, and under similar conditions may be con- 
sidered, like the cost of transportation, to be directly 
proportional to the length of road. 

The saving in cost of maintenance from decreasing 
distance must of course be added to that in cost of 
transportation in order to find the actual value of a 
change of length. 

The value of straightness for a country road is fre- 
quently very much overrated. Considerable devia- 
tions from the straight line may often be made with 
but slight increase in length, and there seems to be no 
good reason for insisting upon absolute straightness. 
The error is commonly made of sacrificing grade and 
expense in construction to the idea of straightness 
without the attainment of any considerable saving in 
length. 

It involves in many cases the injury of the beauty of 
the road and of the landscape, with no compensating 
economic advantages. 



LOCATION OF COUNTRY ROADS, 55 

Art. 18. Rise and Fall. 

By the amount of rise and fall is meant the total 
vertical height through which a load must be lifted in 
passing in each direction over the road. It is distinct 
from and independent of the rate of gradient. 

The minimum amount of rise and fall is found 
where the rise is all in one direction and the fall in 
the other, each being equal to the difference of eleva- 
tion of the terminal points. Any increase in the rise 
and fall beyond this amount is represented by the rise 
encountered in passing from the higher to the lower 
terminus. This may be considered as avoidable rise 
and fall. If the cost of developing the work necessary 
to overcome rise and fall be the same as that of develop- 
ing an equal amount of work to overcome distance, the 
rise and fall may be evaluated in terms of distance, 
and any change in rise and fall may be considered as 
though it were a difference in distance and treated as 
in Art. 17. 

The value of rise and fall in terms of distance will 
depend upon the nature of the road surface, as the 
work necessary to lift a given load to a given height is 
a constant, while the work done in hauling a load over 
a given distance will vary with the resistance offered to 
traction by the surface. Thus, taking the surface as 
above, the work of lifting one ton through a rise of 
I foot is 2000 foot-pounds, while with a tractive force 
of 100 pounds per ton 2000 -f- 100 =20 feet, the 
distance a ton may be moved on the level surface in 
developing 2000 foot-pounds of work. Therefore I 
foot of rise or fall may be considered as equivalent to 
20 feet of level distance, and the value of reducing the 
amount of rise and fall may be found from that for 



56 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

reducing distance. If the road considered were a 
first-class macadam road, with resistance of 40 pounds 
per ton, 1 foot of rise or fall would equal 2000 -f- 40 = 
50 feet of distance. 

Where the rate of grade is less than the angle of 
repose of the wheels upon the road surface (see Art. 2) 
no additional work is imposed, by avoidable rise and 
fall, upon teams hauling loads over the road. The 
amount of work done in lifting the loads up the rise 
is equal to that done by the grade in diminishing trac- 
tion in descending the fall, and the total work required 
is equal to that necessary to haul the loads from one 
terminus to the other upon a uniform gradient. Upon 
an undulating road, therefore, where the grades are 
light, there is no economic advantage in reducing the 
rise and fall of the road. 

When the rate of grade is greater than the angle of 
repose, the amount of work imposed by avoidable rise 
and fall is equal to twice that caused by the excess 
of fall above that at the angle of repose. In this 
case an additional amount of work must be done in 
applying a resistance to prevent the too rapid descent 
of the vehicle in going down the grade. The amount 
of this work in any case equals the work done in lifting 
the load to a height equal to the difference between the 
actual rise of the grade in question and the rise of a 
grade of the same length and a rate equal to the angle 
of repose. Thus on an ordinary earth road whose 
resistance to traction where level is 1 00 pounds per 
ton, suppose a grade to occur of 8 feet per 100, 1000 
feet in length. For the road surface we have 100-7- 
2000 = .05, and the angle of repose is a 5 per cent grade. 
Then 8 per cent — 5 per cent = 3 per cent, or the 
brake-power necessary to secure uniform motion is 



LOCATION OF COUNTRY ROADS. 57 

the same as would be necessary to haul the load up a 
3 per cent grade, and a grade of 3 in 1 00 for 1 000 feet 
gives 30 feet. The work to be done in holding back 
the load for the 1000-ft. grade is therefore the same as 
would lift the load through a vertical height of 30 feet, 
or the fall of 8 feet per 100 for 1000 feet has the same 
effect as 30 feet of rise in the same direction, pro- 
vided brake-power costs the same as animal power. 
The work saved to the traffic passing down this grade, 
by eliminating it as avoidable rise and fall (without 
changing the ruling gradients) , would be twice the above 
amounts or equal to lifting the loads through 60 feet 
of rise. 

Art. 19. Rate of Grade. 

The effect of any change in the ruling gradient upon 
a road depends to a considerable extent upon what 
portion of the traffic may be carried in full loads. The 
lighter portions of the traffic are not so seriously 
affected by heavy gradients as the heavy portions, 
although there is an advantage in light gradients for 
any driving. The rate of speed which may be employed 
will be less upon the portions of the road having heavy 
grade, and the time occupied in a trip over the road is 
therefore affected somewhat by the rate of grade. 

The desirability of a road for general driving is also 
much influenced by the gradients employed, as is 
that value of the road which has for a basis the effect 
it may exert upon the attractiveness of the locality. 
These things all have a certain financial value, which 
of course it is quite impossible to estimate with any 
degree of accuracy, but which should be considered in 
determining the allowable maximum gradient in any 
case in practice. 



58 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

For heavy traffic, such as the transfer of goods from 
one town to another or the marketing of country prod- 
uce, the limitation of load placed upon the traffic by 
the gradient is a matter of importance, the effect of 
which is calculable upon the cost of transportation. 
If in any case the approximate amount of this heavy 
traffic which is likely to be carried in full loads be deter- 
mined, the relative costs of its transportation over 
two lines of differing gradient, other conditions being 
similar, will be nearly proportional to the number of 
loads required to move the traffic over each gradient. 

In estimating the value of reducing the rate of grade, 
it may be considered, as in the case of a reduction of 
length, that its value to the community is represented 
by the saving in annual costs of transportation, and 
that the amount that may reasonably be expended in 
increased cost of construction to effect a reduction of 
gradient is the sum upon which this annual saving is 
the interest. 

The length of a road and the amount of rise and 
fall on it determine the amount of work that must be 
done in hauling a load over the road. The rate of 
gradient, on the contrary, does not affect the amount 
of work necessary to move the traffic, but it limits the 
work that a horse may do at one trip. 

The establishment of a proper rate for the ruling 
grade of the line is, therefore, usually the most impor- 
tant point in location. In localities where light gra- 
dients are easily obtained the problem of location is 
greatly simplified. 

By referring to Art. 3 the comparative loads that 
a horse may draw up different grades will give some 
idea of the importance of carefully considering the 
question of gradient. In nearly all cases in practice 



LOCATION OF COUNTRY ROADS. 59 

there is a considerable latitude within which gradients 
may be chosen. It is usually a question of heavier 
gradients as against greater distance and larger first 
cost for the road. It may be remarked that it is only 
under exceptional circumstances that it is either neces- 
sary or advisable to use a steeper gradient than 5 per 
cent on the new location of a country road of any 
importance. Grades steeper than the ruling gradient 
may sometimes be introduced over short distances 
without impairing the efficiency of the road, as horses 
are usually able to exert for a short time a force much 
greater than they can continuously exert. If the 
length of grade be quite short, 200 or 300 feet, a horse 
can about double his ordinary power in passing it. 

Where long steep grades must be used, it is desirable 
to break them by short stretches of lighter gradients to 
provide resting-places for horses. 

Heavy gradients also have the disadvantage of 
retarding traffic in the direction of falling grade, and, 
as suggested in Art. 18, of requiring the expenditure 
of work to hold the load from too rapid descent. 

Art. 20. Examination of Country. 

For the purpose of obtaining the requisite data 
upon which to base the location of a road, it is neces- 
sary that a careful examination be made of the topo- 
graphical features of the country through which the 
line is to pass. The relative elevations of the termini 
of the line and of intermediate points should be 
obtained, and the directions and steepnesses of the 
various natural slopes determined. 

If a line were to be located connecting points at long 
distances from each other, as sometimes occurs in 



60 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

railway location, it would be necessary to study the 
general configuration of the country, noticing the 
direction of flow of the streams, and the location and 
elevations of the various passes in the ridges through 
which it might be possible to carry the line. Usually 
it would be found that the country is composed of a 
series of valleys, separated by ridges, branching in a 
systematic manner from the main watercourse of 
the region, and that the passes in the ridges occur at 
the head of side streams, and especially where streams 
flowing into valleys on opposite sides of the ridge have 
their sources near each other. 

In the location of common roads, however, the prob- 
lem is ordinarily of a less extended nature, and may 
consist in joining two points lying in the same valley, 
or in joining points in adjacent valleys by a line pass- 
ing over a ridge. In these cases it is only necessary to 
take into account the slope of the valleys in question, 
the positions and elevations of available passes, and the 
side slope of the ridges. 

The slope of the bed of a valley, in hilly country, 
usually forms a concave curve, the rate of slope gradu- 
ally increasing from the lower to the upper end. In a 
valley of considerable length this increase in the rate 
of slope may be very gradual or in short valleys rising 
to a considerable height it may be more sudden. The 
profile ABCD in Fig. II shows the slope of a short 
valley which decreases in slope from about ten feet 
per hundred at the upper end to about two feet per 
hundred at the lower end. 

When a map of the country to be traversed is avail- 
able, showing the positions and elevations of the points 
controlling the location, the work is very much simpli- 
fied, the reconnaissance may for the most part be 



LOCATION OF COUNTRY ROADS. 



61 




62 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

limited to a study of the map, and the routes may be 
sketched upon the map to be tried in the field. If the 
map at hand is an accurate contour map on a sufficiently 
large scale, the entire location may be worked out in 
detail upon the map, leaving only the work of staking 
out the line to be done upon the ground. 

Maps may be obtained, in most parts of this country, 
upon which the horizontal positions of points may be 
readily fixed with sufficient accuracy for the purposes 
of the preliminary examination. Where such maps are 
not obtainable, the positions of points must be ascer- 
tained and a rough map prepared. For this purpose 
directions may be measured with a pocket compass, 
and distances estimated or obtained by the use of an 
odometer or pedometer, as may be most convenient. 

Differences of elevation are easily obtained with a 
fair degree of accuracy by the use of an aneroid 
barometer, and slopes may be measured with a hand 
level. 

Where the rough means ordinarily employed in the 
reconnaissance are not sufficiently accurate to deter- 
mine the controlling points of the lines to be adopted, 
a more complete examination of the country may often 
be made by a rapid topographical survey by means of 
the transit and stadia method. 

Whatever means may be adopted for doing the 
work, the preliminary examination should determine a 
map showing the approximate positions of the con- 
trolling points through which the road must pass, and 
enable a rough sketch to be made of the slopes of the 
country through which the line is to be run. 



location of country roads. 6$ 

Art. 21. Placing the Line. 

Aftef the preliminary examination of the locality is 
complete and the positions and elevations of the con- 
trolling points of the line are known with reference to 
each other, the line must be selected and run in upon 
the ground, or, if the reconnaissance is not conclusive 
as to the position of the best line, it is advisable to 
run in two or more lines and make a more detailed 
comparison between them. 

The controlling points of a line are those points at 
which the position of the road is restricted within 
narrow limits, and is not subject to change. These 
may be points where the location is governed by the 
necessity of providing for traffic, or points where the 
position of the line is restricted by topographical con- 
siderations, such as a summit over which the line is to 
pass a ridge or a favorable location for a bridge. 

Where the line is to be located to a uniform gradi- 
ent, it should be started from the controlling point at 
the end of the grade, which is usually the summit. It 
is then laid off along the slope in such manner as to 
cause it to have continuously the rate of grade decided 
upon. Taking D (Fig. n) at the summit of the valley 
as the controlling point, it is seen that the distance 
from C to D is sufficient to give a gradient of 10 in 
ioo by following directly down the valley, and the line 
with that gradient may be run in that manner. 

The maximum gradient from A to C is, however, 
only 5 in 1 00, and if thought advisable the same maxi- 
mum gradient may be used between C and D by run- 
ning the line DHC diagonally down the slope, as 
shown. This line, having one-half the gradient, will 
have about twice the length of the line CD. 



64 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In running this line it is started from the highest 
point of maximum grade, and points at the surface of 
the ground are continually selected, in advance of the 
placing of the line, which are at the proper elevation 
to permit the grade to pass through them. This may 
be accomplished by setting off the angle of the gradi- 
ent upon the vertical circle of the transit, or upon a 
gradienter, and sighting upon a rod which is moved 
until the line of sight strikes it at the same height from 
the ground that the instrument is setting. The points 
for the line may also be found by running a line of 
levels ahead of the transit line (a hand level is conven- 
ient for this purpose) and pacing distances upon which 
to reckon the gradient, the distances and elevations 
being frequently checked upon those of the measured 
line. 

The location of a gradient upon a common road 
differs from that upon a railroad only in that steeper 
gradients are used, sharper curves or angles may be 
employed, and the gradients need not be lessened on 
ordinary bends or curves. If the line is to make a 
turn upon the slope as at H, the grade should be 
flattened at the turn, and a curve of as large radius as 
possible, without too great expense for grading, be 
introduced. 

In a manner similar to the above a line might be 
run from D on the other side of the valley, which 
using a 5 per cent gradient would give the line DML, 
reaching the bed of the valley at the point L. A lighter 
gradient may be obtained from A to D by starting 
from D and going down by a continuous gradient of 
4 in 100 on the line DFGA, and greater or less rates 
of descent may be adopted and lines corresponding to 
them located, as may be considered advisable. 



LOCATION OF COUNTRY ROADS. 65 

The center-line for a final location should be care- 
fully run, and points permanently marked from which 
it may be relocated when necessary. An accurate line 
of levels should also be run over the center-line and a 
profile drawn, upon which the grades may be estab- 
lished and earthwork estimated. 

After placing the center-line, topography should be 
taken carefully upon each side of the line for some 
distance, and a map drawn showing the topography 
and giving elevations by means of contours. This will 
serve to show whether the line is placed to the best 
advantage, and whether any changes are desirable. 
This is especially necessary over rough ground or 
where the line is on maximum gradient, as frequently, 
and perhaps usually, the first line run will be useful 
only as a preliminary line, which with its accompany- 
ing topography will permit a proper location to be 
made. 

Art. 22. Comparison of Routes. 

In selecting a line for the construction of a road the 
principles already mentioned in the early part of this 
chapter should be had in mind. The line must be well 
designed to accommodate the traffic. It should have 
as easy grades, short length, and small rise and fall as 
is consistent with a reasonable cost of construction, in 
order to give light costs for transportation and for 
maintenance. 

Suppose in the case shown in Fig. 1 1 that it is desired 
to connect the village at the point A with the point D 
and with the roads leading through the passes at F 
and /. Which line it will be the most advantageous 
to adopt depends upon the relative importance of the 
traffic to the various points considered. 



66 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

The shortest, and probably cheapest, line from A 
to D would be obtained by following the valley over 
the line ABCD, which line, as shown by the profile, 
would give a maximum gradient of 10 in ioo between 
C and D. The line FB joining the first line at B 
would afford communication with the summit at F 
with a maximum gradient of 5 in 100. If the traffic to 
the point D be small and unimportant, so that addi- 
tional expense in reducing the gradient from C to D 
is unadvisable, these lines might prove a satisfactory 
location. 

If, however, D be a point of importance and the 
traffic from A to D heavy, it will be necessary to adopt 
some means to reduce the gradient from C to D. 
Leaving out of consideration the point F and consider- 
ing B and C as points of minor importance, it might 
be advisable to use the line ALMD with a uniform 
5 per cent gradient from D to L, and branches to 
connect with C and B. This would give a line but 
little longer than the valley line, with only ope-half the 
ruling gradient of that line. 

If C is not important and can be neglected while B 
and F must be considered, the line ABEHD has a 
maximum gradient of 5 in 100, and connects A with 
the points BF and D with a minimum total length of 
road (being less than the valley line first considered). 

When B and C must both be considered as of im- 
portance as well as F and D, the lines ABCHE and 
HD will give a ruling gradient of 5 in 100 to both F 
and D, and passing through B and C with a somewhat 
longer line than in the last case. 

This arrangement would make the length of haul 
from A to D and F each longer than by the first line 
considered; but the gradient to D would be lighter, and 



LOCATION OF COUNTRY ROADS. 67 

the total length of road to be constructed and main- 
tained would be less. 

In case the points B and C are both unimportant, 
and the line through the valley may be neglected, the 
line AGFD provides a ruling gradient of 4 in 100 from 
A to both F and D, and connects them with each 
other, with about the same length as the shortest 5 per 
cent gradient. When the point / must be taken into 
account, this line may be connected with / by the line 
GI having a gradient of 4 in 100. This would give the 
shortest line of uniform gradient to connect A with the 
three points /, F and D, and possibly a desirable line to 
construct when the line through the point / is impor- 
tant, even if the valley road from A to B is also neces- 
sary. 

The lines upon the side slopes are usually more ex- 
pensive to construct than the valley lines, and the dif- 
ferences of first cost of the various lines must of course 
be considered. The importance of a difference in ex- 
pense of construction depends upon the traffic to be 
hauled over the road and the kind of surface to 
be used. Where a broken-stone or gravel road is to be 
constructed at considerable expense, the difference of 
cost due to a change of location is relatively less 
important as being a less percentage of the whole cost, 
while the difference of tractive effort due to grade is 
of more importance, as being a higher percentage of 
that upon the level, than would be the case with an 
ordinary earth road. 

As is easily seen from the above the choice of a 
location for a road, while depending upon principles 
easily stated, is in reality a matter requiring the use of 
judgment, and is not readily reducible to a financial 
comparison stated in money values, because the data 



6$ A TEXT-BOOK ON ROADS AND PAVEMENTS. 

concerning the volume of the traffic and the cost of 
conducting it can be determined only very roughly, 
and contains many elements of error. For purposes of 
comparison to aid the judgment, approximate data 
may often be assumed or determined by a study of the 
localities affected. In some cases observations may be 
made of the number of teams of different classes pass- 
ing certain points within certain times, to give a basis 
for estimation of the annual volume of traffic. In 
other cases, the annual hauling traffic, which is usually 
the most important portion of the traffic in considering 
location, may be estimated from the known interests of 
the locality. Thus, if the produce of a certain section 
of farming country must be hauled over a given road 
to market, the amount of this produce may be esti- 
mated from the acreage, and the relative number of 
loads upon different grades then determined. The 
cost per load over the road would then need to be as- 
sumed in order to find the annual value of a reduction 
of grade. 

In the same manner, the effect of changes of length 
and in the amount of rise and fall may be found as 
indicated in Arts. 17 and 18. 

All of these items must be combined to find the rela- 
tive total costs of transportation for each route. The 
cost of construction and of maintenance for each line 
must then be estimated, and that line is the most ad- 
vantageous which makes the sum of the annual charges 
and the interest on the first cost a minimum. Where 
several lines of traffic are to be considered together as 
in Fig. 11, the cost of conducting all of the traffic by 
each system of lines that may be employed must be 
considered, the entire cost being made a minimum for 
the system to be adopted. 



LOCATION OF COUNTRY ROADS. 69 

Art. 2$. Changing Existing Locations. 

The problem that arises oftener than any other 
in country-road location is that of improving short 
stretches of road, where, owing to defective location, 
the grades are unnecessarily heavy, the length unneces- 
sarily great, or the ground over which the road may 
pass such as to make its maintenance in good con- 
dition difficult and expensive. The first of these is 
the most common defect of ordinary country roads, as 
shortness of distance has very commonly been obtained 
by the disregard of the desirability of light gradients, 
which in very many cases are easily obtainable. 

The principles to be observed and methods of pro- 
cedure in making the new location are exactly the 
same as in an original location, save that in this case a 
road already exists, and the question of economy is one 
of determining whether the advantages to be gained 
in lessened costs of transportation and maintenance 
is sufficient to warrant the expense of obtaining new 
right of way and constructing new road. 

In Fig. 12 is given an example that is frequently met 
in practice, where the existing road abed runs over the 
point of a hill, with heavy gradient, while a line of very 
much lighter gradient might be located around the 
base of the hill through the pass at e, giving a greater 
length of road, but much less rise and fall. The line 
bed in the figure has a length about 800 feet greater, a 
rise and fall 70 feet less, and a maximum gradient one 
half as steep as the line bed. These relations are shown 
in the profile in Fig. 12. 

If the road in question be a common earth road, 
I foot of rise and fall may be taken as equivalent, in the 
work required to haul a load over it, to 20 feet of dis- 



JO A TEXT-BOOK ON ROADS AND PAVEMENTS. 





P 


O 
O 






c 

r 


> 






c 


1 




/ 






















I 




o 


























1 


/ 




























1 


/ 




. N. \V 






















/ 




/ 




























h 




^ 


\1sX \AW(| ///// 


















/ 


1 




8 
















/ 
/ 


f 

/ 


1 




O 

CM 




^fcNS^S\\^W/ //// 














I 


/ 








O 

P 
























o 




























to 
















// 




























i 






















J 


/ 
















o 

O 






/ 


















O 


\\ 






/ 


f 


















"t 


fc 


MM 




/ 

i 






\ 

\ 

• 














8 




\ 






i 
/ 














8 


ij 






\ 






i 
I 
I 














o 














i 














Q 










/ 














O 




^yy^ 


js^ 
























CD 


fT ^ 




^s / / // / 




























'///// ^— — 










i 


















S S \r / y^ — 










/ 














O 




Ss S^ S X 










/ 














© 










/ 














o 




/ j^ y^ s 


o 








/ 






< 


■) 






ts 


,-r-^lK^ 




o 

2-. 






J 


•8 






< 
< 


4 









2 



LOCATION OF COUNTRY ROADS. 7 1 

tance, and the 70 feet saved by the new location would 
be equivalent to 1400 feet of distance. Hence, the 
line bed may be considered as having an equivalent 
length for purposes of traffic 1400 — 800 = 600 feet 
shorter than the line bed. In addition to this, loads 
may be taken over the new line in direction b to d 
more than double, and in direction from d to b triple, 
in weight those that can be taken by the same power 
over the old line. 

A further improvement of the line -may also be 
possible, if the new line can join the old one at a point 
lower down than b, by running a lighter gradient than 
5 in 100 from the point e. Thus the line efa would 
give an uniform gradient of 4 per cent, but would 
require the construction of more new line. 

In considering changes of location, it is also neces- 
sary to take into account the interests of adjoining 
owners. Houses and buildings are largely located with 
reference to the existing position of the roads, and 
changes in the position of a road may involve injury to 
such property. The question then becomes largely 
one of sacrificing the interests of the users of the road, 
or those of the adjoining owners — a question that 
should be, but commonly is not, decided by consider- 
ing what will be of most advantage to the general com- 
munity. 



CHAPTER IV. 

IMPROVEMENT AND MAINTENANCE OF COUNTRY ROADS. 
Art. 24. Nature of Improvements. 

Ordinary country roads may be classified as earth 
roads, gravel roads, and broken-stone roads. The 
larger number of common roads throughout this coun- 
try belong of necessity to the first class. In a few of 
the more enterprising communities the more important 
roads are constructed of gravel or broken stone. 

The percentage of roads of the better class is, how- 
ever, very small, and although there has recently been 
a distinct improvement in this particular, the inability 
of rural communities to at once raise the funds neces- 
sary for the general construction of first-class new 
roads will cause their increase to be very gradual. 

Improvement in country roads may be of several 
kinds : 

(1) Changes in location, by which better alignment 
or better gradients may be obtained, or by which the 
natural conditions of surface or drainage may be im- 
proved. This has been discussed in Chapter III. 

(2) Reconstruction of the road-bed, as in regrading 
steep slopes to give lighter gradients, or in raising the 
road-bed across low and wet places to provide for 
drainage. 

(3) The construction of artificial drainage where a 
road is built over ground which is likely to become soft 
in wet weather, or where water may reach the road-bed 

72 



IMPROVEMENT OF COUNTRY ROADS. 73 

from underground sources. This has been discussed in 
Chapter II. 

(4) Improvement of the surface, which may consist 
in re-forming the surface of natural earth, or in the 
construction of an artificial surface or pavement, the 
latter of which will be discussed in separate chapters. 

The more important lines of travel leading out from 
the towns will gradually be improved by the con- 
struction of broken-stone or other permanent roads, but 
this constitutes but a small percentage of the total 
mileage, and the problem in common-road improve- 
ment is for the most part that of making the most of 
the roads that exist, rather than reconstructing them 
with new material. The materials and funds imme- 
diately available must be used to secure as much im- 
provement as possible. 

Earth roads, under the most favorable conditions, 
do not usually attain a high degree of efficiency, and 
are not economical under any considerable traffic. 
They are, however, capable of much improvement and 
need not become, as they frequently do, practically 
useless during a large portion of the year. This im- 
provement must be gradual and come about through 
the adoption of more rational methods of maintenance, 
rather than through immediate reconstruction of the 
road surfaces. 

Art. 25. Grade and Cross Section. 

As already explained in Art. 10, the drainage of the 
surface of a road is accomplished by crowning the sur- 
face and giving it a proper longitudinal slope. Under- 
drains will not drain water from the surface of the road, 
and unless the crown is at all times maintained and the 



74 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

surface kept smooth, water is likely to stand upon the 
surface and soften it. 

Grade. The surface of a country road should not be 
level in the direction of its length, but should have a 
sufficient longitudinal slope to drain any water from 
its surface which might otherwise be held by small ruts 
or depressions. The minimum grade for an earth 
road should be at least \ foot in 1 00 feet, and for a 
broken-stone road nearly as much. The grade, except 
in very rough country, should not exceed 4 or 5 feet 
per 100, and when steeper grades are necessary, they 
should be made as light as may be feasible. The effect 
of changing the rate of grade is discussed in Art. 19. 

Width. Too great width of roadway upon country 
roads causes an unnecessary expense in the con- 
struction and maintenance of the road, and the width 
should be only sufficient to provide space for the 
easy conduct of the traffic. For roads of ordinan^ 
traffic, this requires only that there be room for teams 
moving in opposite directions to freely pass. A 
width of 20 feet is ample for most country roads, and 
for roads of lighter traffic 16 feet is often sufficient. 
Outside of this width, side ditches must be formed for 
carrying the surface drainage. 

In the construction of gravel or broken-stone roads, 

Fig. 13. 

the paved portion of the road does not usually extend 
to the full width of the roadway, a shoulder of earth 
being left on each side, as shown in Fig. 13. The width 
of broken stone on ordinary country roads may vary 



IMPROVEMENT OF COUNTRY ROADS. 75 

from about 12 feet to 16 feet. A greater width than 
this need only be employed on important roads which 
convey large traffic, or on city streets. 

While the improved portion of the road should be 
as small as is consistent with the proper discharge of 
the duty required of it, the available right of way need 
not be so restricted, but should be laid out wide 
enough to permit of the widening of the used portion 
when necessary, and allow room at the sides for pedes- 
trians, with a grass border and line of trees. When 
trees are planted along the roadway they should not 
be placed so as to form a dense shade over any portion 
of the traveled road, although a moderate shade is 
not a disadvantage, and care should be used that they 
are not near enough to a covered drain to permit the 
roots to grow into the drain and choke it. 

Crown. The surface of a road must be crowned 
sufficiently to cause the water which falls upon it to 
run at once into the gutters. The height of crown 
required depends upon the character of the surface and 
upon the grade of the road. A high crown is objec- 
tionable because it concentrates the travel in the middle 
of the road, which tends to wear hollows longitudinally 
along the road into which water may settle; but if 
the crown be too low, small depressions worn into the 
surface by the traffic may hold water and cause the 
road to become soft. The slope from the center to 
the side of an earth road should not be less than one 
in twenty nor greater than one in ten, corresponding 
to a height of crown from one-fortieth to one-twentieth 
of the width of the road. For roads upon which the 
surface can be kept in smooth condition and on 
moderate grades, the lower limit may be used, but on 
the average country road a steeper slope is desirable 



76 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and a crown of one-twentieth the width is not too 
great to secure efficient drainage. 

Gravel and macadam roads should be crowned 
somewhat less than earth roads. On wide macadam 
streets kept in smooth condition, the side slopes may 
be as low as one in thirty, or a crown equal to one- 
sixtieth of the street width. On such work, however, 
it is more common and probably better to use a crown 
of one-fiftieth, or even one-fortieth the width; while on 
ordinary graveled or macadamized country roads the 
crown should be from one-thirtieth to one-twenty- 
fourth of the width. When constant attention and 
careful maintenance can be relied upon to -keep the 
surface in smooth condition a less crown may be used 
than would be allowable if the road is likely to be 
subjected to considerable wear between periods when 
repairs are made. 

Form of Section. There is considerable difference of 
opinion amongst road builders as to the best form to 
give the surface of a road. Some use a section com- 
posed of two planes of equal inclination rounded off in 
the middle and sloping uniformly to the sides as shown 
in Fig. 14. Others prefer to use a convex curve, 

Fig. 14. 

approximately the arc of a circle, or more commonly, 
a parabolic curve, which is practically identical with 
the circular arc. The exact form is not a matter of 
importance on a country road, and either of them, or 
some intermediate form, may give good results in 
practice. It is not desirable to insist upon great 



IMPROVEMENT OF COUNTRY ROADS. TJ . 

accuracy in the form of section provided a proper 
crown be given and the surface be properly smoothed. 
Where a smooth pavement is used, however, it is 
desirable to place it accurately to a uniform section. 
Gutters. At the side of the road longitudinal ditches 
must be provided for the purpose of carrying the water 
drained from the surface of the road to some point , 
where it may be turned into a natural drainage channel. 
In many instances these side ditches also carry the 
drainage from land adjacent to the road. The size 
and form of the gutters will naturally depend upon the 
quantity of water to be carried and the slope of the 
gutters. In some instances the extension of the road 
surfaces, as shown in Fig. 13, will be sufficient and no 
special gutters will be required. In deep cuts where 
the excavation necessary to form side ditches would 
be expensive, a tile may be placed under each side* of 
the road, as shown in Fig. 16, into which the drainage 



.Tile 



OTile 



Fig. 16. 



from above the cut and from the small gutters may 
be carried. 

Broad, shallow gutters are, in general, to be pre- 
ferred to deep and narrow ones. The side slopes 
should not, in any case, be less than 2 horizontal to 
I vertical, and 4 or 5 to I , on the side next to the road- 
way, is better. Shallow gutters are easier to form and 
keep clean, and are not so likely to wash out at times 
of heavy rainfall. It is not desirable to use deep side 



78 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

ditches for the purpose of under drainage, and water 
will not be drawn from the surface of a hollow roadway 
into such ditches. Fig. 17 shows a common form 
where it is intended to use the side ditches to prevent 
any seepage of water from the sides to the road-bed. 




Fig. 17, 

This is the standard section given for state aid roads 
in New York, using a ditch two feet deep with side 
slopes two to one. This form is also used by the 
Massachusetts Highway Commission, who recommend 
ditches 3 feet deep, I foot wide at bottom and with 
slopes 2 to I. Fig. 18 shows section recommended 
by the Illinois Highway Commission for use in level 




miiliiiiiiiiiiiiint. 



Fig. 18. 



-»<— -s - — -^ — -a'— -->• 



.L. -I 




country, where the roadway is formed by material 
excavated from the side ditches. 

On the average country road, surface drainage will 
be amply secured by gutters 18 inches to 2 feet below 
the crown of the roadway, and side ditches of greater 
depth are a source of unnecessary expense. Where 
under drainage is necessary it should be accomplished 
by tile or other covered drains. 



improvement of country roads. 79 

Art. 26. Earthworks. 

• 

Improvements to the road-bed of an existing coun- 
try road may have for their object the reduction of 
gradient upon steep inclinations by cutting the material 
from the road-bed and lowering the surface of the 
road on the upper part of the grade, and filling in 
correspondingly on the lower part, or they may be 
intended to provide better drainage by raising the 
road across low ground. 

In the construction of new roads, the formation of 
the road-bed consists in bringing the surface of the 
ground to the grade adopted for the road. This grade 
should be carefully established upon an accurate pro- 
file of the line, in such manner as to give as little 
earthwork as possible, both to render the cost of con- 
struction low, and to avoid unnecessarily marring the 
appearance of the country in vicinity of the road. 
The most desirable position of the grade line is usually 
that which makes the amounts of cut and fill about 
equal to each other, especially where room for borrow- 
pits, or spoil-banks, would be expensive, and it is 
desirable to make the embankment for the most part 
of the material taken from the road excavations. On 
side-hill work, one side of the road is commonly in cut 
and the other in fill, and where the side slopes are 
steep, it is usually better to make the road mostly 
in cut on account of the difficulty of forming stable 
embankments on steep ground. In balancing cuts and 
fills, it is necessary to estimate the quantities for the 
full width, including side ditches, as the grade should 
be placed high enough to permit using the material 
cut from the ditches in the embankment. 

Shrinkage. Earth, in embankment, will compact 



80 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

closer than it is found in its natural state, and allow- 
ance for shrinkage must be made in estimating the 
amount of excavation necessary to form a given 
embankment. On an average, ordinary soil may be 
expected to shrink 10 to 12 per cent of its bulk; gravel 
or sand will shrink a little less than this, 8 or 9 per cent; 
light surface soils a little more, 14 or 15 per cent. 
The shrinkage may also be somewhat affected by the 
method of construction used in forming the embank- 
ment, being slightly less for work placed by wagons 
than for that by scrapers, and still less for wheelbarrow 
work. 

Settlement. In forming an embankment, allowance 
must sometimes be made for subsequent settlement, 
by raising the top of the embankment above the 
required grade. Where scrapers are used, the earth 
will usually be well compacted in placing, and no 
allowance is necessary; with dump carts or wagons the 
compacting is not so thorough, and a small allowance 
should be made; while when wheelbarrows are used or 
the earth is thrown into place with shovels, an allow- 
ance of 10 or 12 per cent must be added to the height 
of the embankment, in order to allow for the final 
shrinkage. Rock occupies more space in embank- 
ment than in excavation, and does not need allowance 
for shrinkage. 

Embankments. When embankments are to be con- 
structed, brush and weeds should be removed from the 
site and at points where the filling is thin, it is desirable 
to remove all vegetable matter and soft material, to 
prevent unequal settling and the formation of soft and 
spongy places in the surface of the road-bed. 

In constructing embankments across wet and 
unstable ground, it is frequently necessary to form an 



IMPROVEMENT OF COUNTRY ROADS. 8 1 

artificial foundation upon which to place the earth- 
embankment. This may be accomplished in some 
cases by excavating a little of the soft material and 
substituting sand or gravel, or in other cases it may be 
advisable to employ layers of brushwood or fascines 
as a support for the enbankment. Sometimes it may 
be possible to drain the soft material by deep ditches, 
so as to render it capable of sustaining the road, and 
in all cases drainage should be provided in so far as 
possible to make the embankment more secure. 

When embankments are to be found on sloping 
ground, the surface of the ground should be stepped 
off, in order to hold the earth-filling from sliding upon 
the natural surface at the line of contact between the 
two, until it becomes sufficiently settled for the develop- 
ment of cohesion to cause it to become one solid mass. 

In many cases where roads are to be constructed 
along steep slopes, it is found cheaper to use retaining 
walls to sustain the road upon the lower side and the 
earth cutting on the upper side than to cut long slopes 
or form high embankments. 

Catch-water drains are necessary on the natural sur- 
face above the top of all high slopes in cuttings to 
prevent the surface water from washing down and 
destroying the face of the slope. 

Where springs are tapped by a cutting, drains must 
be provided to remove the water without injury to 
the slope; and where the subsoil may become wet in 
rainy weather, it may be necessary to provide sub- 
surface drains along the slope to prevent the earth 
becoming saturated and sliding down into the roadway. 

Slopes, both of excavation and embankment, are 
greatly improved by being sodded or sown with grass. 
This aids in the maintenance of the slopes, by render- 



82 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

ing them more capable of resisting the abrading action 
of such water as falls upon them. It also greatly 
improves their appearance. 

The most important principle involved in the forma- 
tion of a road-bed, which should be always in mind, is 
that earth, in order either to sustain a load or to main- 
tain a slope, must be kept dry, or at least prevented 
from becoming saturated with water, as both the 
cohesive and frictional resistances of earth are dimin- 
ished or destroyed when it becomes wet, and it is also 
then liable to the disturbing action of frost. 

Methods of Handling Earth. In the grading of roads 
or streets, the earth is commonly moved by scrapers, 
or wagons, after being loosened by plowing. For 
ordinary work the common railroad plow is used, drawn 
by two, or in hard material four, horses. In breaking 
up very hard material, like an old gravel surface, a 
rooter plow may be needed with four or six horses. 
Economical handling of the material requires that it 
be well loosened and the plowing is usually but a small 
part of the cost. 

For moving the loosened earth, drag scrapers may 
be used for short hauls; they are economical for 
distances up to about ioo feet. For distances greater 
than about 80 to 100 feet wheel scrapers will be more 
economical; for the shorter hauls, the small (number 1) 
scraper, with a single team to handle each scraper; 
for longer hauls, above 200 to 300 feet, the larger 
(number 3) scrapers, with snatch teams to load them. 
For hauls greater than about 500 to 600 feet, wagons, 
loaded by men with shovels, will usually be cheaper 
than scraper work. 

In flat country where the grades conform closely to 
the natural surface, and the road-bed is formed with 



IMPROVEMENT OF COUNTRY ROADS. 83 

earth taken from the side ditches, the use of the eleva- 
ting grader is usually economical and frequently makes 
possible the construction of the road at very low cost. 
This consists of a frame resting upon four wheels, 
from which is suspended a plow and a wide traveling 
belt. The plow loosens the earth and throws it upon 
the inclined belt, which carries it to one side and de- 
posits it near the middle of the road. The ordinary 
machines are built to deliver the material at about 14 
and 17 feet horizontally from the point at which it 
is excavated. They are usually operated with eight 
horses. 

The ordinary road machine, or scraping grader, is 
also a convenient tool for this kind of work, and when 
the amount of material to be moved is small, and the 
work consists in cutting shallow side ditches and form- 
ing a road surface with material taken from them, Is 
usually the most economical tool to employ. 

Work done by scrapers will usually be left in rough 
and lumpy condition. For smoothing the surface, 
after the earthwork is roughly completed, the scraping 
grader or some form of road leveler may be used. For 
this purpose the blade is set so as to cut off the tops 
of the ridges and lumps, and fill up the hollows, with- 
out carrying along any earth. 

Work Required in Moving Earth. The work 
required for moving earth under approximately the 
same conditions differs widely in practice. It depends 
upon the character of the material, the methods 
adopted for the work, the kind of labor available, 
and, most important of all, the skill with which it is 
managed. 

Loosening. In ordinary compact soil a plow and 
team with driver and plow holder will loosen 30 to 40 



84 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

cubic yards per hour. If the material be very hard, 
an extra team and man will be required for about the 
same, or a little less, amount of earth; while in hard 
buckshot, or in breaking up an old road surface, not 
more than one-half the amount may be loosened. 

Drag Scrapers. On short hauls up to about 50 
feet, a team with drag scraper may handle from about 
4 to 7 cubic yards per hour, and one man will load 
for 2 or 3 scrapers, depending upon the distance. 
If the lead be 1 00 feet, the drag scraper should move 
from 3 to 5 cubic yards per hour, and one man should 
load about 4 scrapers. 

Wheel Scrapers. Small (number 1) wheel scrapers 
have a capacity of about \ cubic yard of compacted 
earth, and for a haul of 100 feet may be expected to 
give about the same results as drag scrapers. For 
longer hauls, about one minute of time of team and 
driver will be required per trip for each 100 feet of 
additional distance, or about 5 minutes for each yard 
of material moved. 

The large size (number 3) wheel scraper may be con- 
sidered as carrying J cubic yard at a trip. A snatch 
team and extra man, or two extra men, will be required 
to load. These will load a scraper in an average of 
from one minute to two minutes. Two or three min- 
utes may be allowed for loss of time of scrapers on each 
trip in loading and unloading, and one minute for 
each 100 feet of haul. Thus, with a lead of 300 feet, 
a trip would be made in five or six minutes; 10 or 12 
trips per hour, or from 3J to 4 cubic yards per hour 
for each scraper. 

Wagons. Over ordinary earth roads a team and 
wagon will carry an average load of 1 cubic yard; on 
good hard earth roads i\ yards may be taken. In 



IMPROVEMENT OF COUNTRY ROADS. 85 

loading ordinary soil which has been loosened by plows, 
men may be expected to average from ij to 2 cubic 
yards per hour. When the work is fairly well organized 
and as many men are employed in loading as can con- 
veniently work about a wagon (usually about 7 or 8) 
the loss of time of each team in loading, unloading, etc. 
may average about 5 to 7 minutes for loads of one cubic 
yard, while the time occupied in hauling will average 
about one minute for each 100 feet of lead. When dump 
wagons are used, about one minute would be saved 
on each trip. 

In estimating the cost of earthwork, about 20 to 25 
per cent should be added to the labor cost for con- 
tractor's profit, contingencies, etc. The skill with 
which earthwork is managed has much to do with the 
cost. Failure to properly organize and systematize 
the work may easily increase the labor cost 50 per 
cent. It is not uncommon to find that two pieces of 
work identical in character, and conducted under the 
same conditions, differ 25 per cent in cost, because of 
the difference in the foremen handling the work. 

Art. 27. Earth Roads. 

The maintenance of an earth road surface in good 
condition consists in keeping it crowned and smoothed, 
so that water which falls upon the surface flows away 
immediately into the gutters without remaining upon 
the road long enough to do serious harm in softening it. 
If ruts and depressions are allowed to form in the road 
surface, they will hold water until it is absorbed into 
the road or evaporated, thus softening the road so 
that wheels will cut deeply into it, and gradually 
destroy its firmness. 



$6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

The improvement of an earth road surface which is 
not in good condition must, therefore, be effected 
mainly by reshaping it into a form with proper crown 
to shedthe water. Its subsequent maintenance requires 
that it be frequently smoothed to prevent the forma- 
tion of ruts. It is practically impossible to maintain 
an ordinary earth road in good condition by the 
method of annual repairs. Where this method is 
followed, the road is usually shaped up with a road 
grader, after it dries sufficiently in the spring, and 
may present a good surface during the summer and 
fall. It will, however, be worn hollow by the time 
bad weather sets in, and will be in condition to hold 
water and become saturated by heavy rains or melting 
snow. 

Shaping Section. The form of cross section which 
should be used has already been discussed in Art. 25, 
and the drainage of the road should be provided for 
where necessary as described in Chapter II. For 
cleaning the side ditches and forming the surface of 
the road, the ordinary road grader, or scraping grader, 
is used as mentioned in Art. 26. In this work, the 
blade of the grader is set so as to carry the material 
from the ditches toward the middle of the road, and 
repeated trips are made until the proper crown is given 
to the road surface. In doing this, care should be 
taken not to leave a ridge of soft material at the middle 
of the road, but to spread it evenly so that travel may 
take any part of the road surface, and thus compact it 
evenly. This may be accomplished by slightly raising 
the end of the blade of the grader nearest the middle 
of the road. In using the grader, the amount of 
material moved and its distribution are controlled by 
changing the angle at which the blade is set, and the 



IMPROVEMENT OF COUNTRY ROADS. 87 

elevation of its ends. Experience in handling the 
machine is necessary to its skillful use, and the amount 
of work required in forming a road is largely dependent 
upon the skill and experience of the man operating 
the machine. Good results in such work also require 
that the teams used be well broken to the work. 

Where roads are shaped in this manner in the spring, 
the work should be done before the surface has become 
dry and hard, and while the earth is in condition to 
pack and unite with the surface upon which it is placed. 
After the ground has become dry and hard, the work is 
more difficult and expensive, and the road is usually 
left in bad condition because the material moved, 
being hard and lumpy, does not pack readily under 
travel. 

Smoothing Surface. The maintenance of an earth 
road in good condition requires that surface be fre- 
quently smoothed so as to prevent the formation of 
ruts, which may hold water when rain comes. Repair- 
ing the road by reforming the surface when it has 
gotten out of shape may improve it so that it will 
remain in fair condition so long as weather conditions 
are favorable, but when rain comes the surface will be 
softened so that wheels cut in to a small depth, making 
small indentations. These, if allowed to remain, will 
hold water at the next rain, causing the road to become 
soft to a greater depth and deeper ruts to form. If, 
however, after each rain the road be smoothed out, 
eliminating the ruts, and moving a little earth toward 
the middle of the road to replace that lost through 
wear, the road surface will be hardened and improved 
at each treatment, and will not retain water when con- 
tinued rains come upon it. 

The smoothing of the road surface should be done 



88 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

when the road is drying out after a rain; when it is 
not too muddy, but before it has become hard. The 
earth is then in condition to pack readily under travel, 
and will form a smooth hard surface when it becomes 
dry. If undertaken when the surface is too wet, it 
may be muddy and sticky to work; after it becomes 
dry, no good can be accomplished by working it, as it 
will not pack smooth and hard. When a road is kept 
shaped up by smoothing it after each rain, the earth 
composing the road surface becomes puddled, through 
being worked while wet, until it becomes practically 
impervious to water and forms a very hard crust on the 
surface. This effect is observed upon all soils which 
soften upon absorbing water, and become hard when 
dry, but is most noticeable upon clay or other heavy 
soils. The soil which makes the worst and most 
sticky mud when allowed to become saturated with 
water makes the hardest and most impervious surface 
when well maintained. 

Methods for Smoothing Surface. Several methods 
have sometimes been employed for smoothing the 
surface of an earth road. For the purpose of smoothing 
out the ruts in the spring, when a muddy road is drying 
up, a railroad rail 12 to 1 6 feet in length has sometimes 
been used, the rail being drawn by teams hitched at 
the ends so as to cut off the ridges and fill the ruts. A 
heavy stick of timber faced with steel on one edge has 
also been used in the same way. These methods may 
prove quite efficient at times when the roads are in bad 
condition, causing the surface to dry smoother than 
would otherwise be the case. 

The scraping grader is frequently used for light 
trimming of the surface, but is not usually an economical 
tool to use unless heavier work is to be done, on account 



IMPROVEMENT OF COUNTRY ROADS. 89 

of the weight of the machine and the cost of operating it. 
Several types of light road scrapers, or road levelers, 
as they are usually called, requiring only a single team 
and driver, or perhaps also a man to operate the 
machine, are occasionally used for this purpose. These 
levelers are sometimes mounted upon two wheels, and 
the blade made adjustable in position; others are simply 
cutting blades which slide upon the ground in fixed 
position. They frequently do good work in smoothing 
the surface when the soil is in .proper condition, 
although they do not pack the material upon the 
surface of the road. 

Road Drag. The cheapest and most successful 
method yet devised for maintaining the surface of a 
road in good condition is by the use of the road drag. 
This method has been used with great success in the 




Fig. 19. 

states of the Mississippi valley, where the maintenance 
of earth roads in condition to be used at all seasons 
had previously been considered an almost hopeless task. 
Its introduction is largely due to the efforts of Mr. 
D. Ward King, of Maitland, Mo., who spent most of 
his time for a number of years in introducing and 
explaining his method of using the "split log drag." 
Fig. 19 shows a drag as commonly constructed of split 



90 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

logs. The following description of the drag and its 
operation is taken from the report of the Illinois 
Highway Commission for 1906: 

"The log should be from 10 to 12 inches in diameter 
and about 9 feet long. The holes in the front half of 
the log should be bored so that a slight slant forward is 
given to the lower part of the front face of the split log. 
The holes in the rear log are bored so that its flat face 
will be perpendicular to the sticks forming the con- 
necting braces which should be tapered at the ends 
so that they will fit snugly into the holes bored into the 
logs. The holes should not be less than two inches in 
diameter. The ends of the cross sticks should be 
split and wedges driven so as to secure the cross braces 
in place. The wedges should be driven crosswise of 
the grain of the log or plank so as not to split it. A 
diagonal cross brace is placed between the logs at the 
leading end to stiffen the frame of the drag. The 
distance from the face of the back log to the face of the 
front log should be about three feet. The lower front 
edge or toe of the drag should be protected by a strip 
of old wagon tire, or other piece of iron, about a quarter 
of an inch thick and 3 or 4 inches wide and about 4 
feet long. This strip of iron should be bolted to the- 
front log and the heads of the bolts countersunk. The 
strip of iron should not be carried the entire length of 
the front log. 

"Chains should be provided with which to haul the 
drag, arranged with a short and long hitch as shown in 
the sketch, so that the drag will travel at an angle of 
about 45 degrees with the direction of the road. It 
will be noticed from the sketch that the long hitch of 
the chain goes over the log around one of the cross 
pieces rather than through a hole in the front log. 



IMPROVEMENT OF COUNTRY ROADS. 9 1 

This allows the earth to slide unobstructedly along the 
front face of the drag. " 

The drag may also be made of planks, instead of 
logs; 2 by 12 inch planks are used for this purpose, 
reinforced on the inner side by 2 inch by 6 inch strips, 
to provide a greater thickness of wood through which 
to bore the holes. 

" When the road drag is properly used it spreads out 
the layer of impervious soil over the surface of the road, 
filling up the ruts and hollows until a smooth surface is 
secured. As a small amount of material is always to be 
pushed to the center, a slightly rounded effect will be 
given to the road, which may be increased or decreased 
as desired by subsequent dragging. By forcing the 
mud into the hollows and ruts, it is evident that the 
water must go out, which it does by running off to the 
side of the road. The drying out of the road is thus 
much facilitated and the road is made immediately 
firmer because the water is squeezed out. 

"The effect of traffic over the road tends to press 
down and thoroughly compact the top of the road and 
each thin layer of puddled earth which the drag 
spreads over the surface every time it is used. After 
the first few draggings it will be noticed that the road is 
becoming constantly smoother and harder so that the 
effect of a rain is scarcely noticeable, the water running 
off the smooth hard surface which absorbs but little of 
it." 

The action of the drag differs from that of an ordi- 
nary scraper or leveler in that it packs the material 
upon the surface, while the leveler merely smooths the 
road by trimming off the high places and distributing 
the material into the low places. 

Constant attention is necessary to maintain an 



92 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

earth road in good condition, The dragging should 
be done as soon after each rain as possible., and at all 
seasons of the year. If dragging is done before a 
cold spell, the road will freeze in a smooth condition, 
and will be in good condition when the frost leaves it. 

The amount of work required in dragging roads is 
comparatively small. While frequent attention is 
necessary, the work to be done at one time is insignifi- 
cant. In several instances it has been found that the 
cost of maintenance by dragging is much less than the 
expenditure previously incurred for shaping up the 
road with the grader in the spring. 



SAND ROADS. 

When a road surface is composed of sand, it will be 
more firm when the sand is damp and more unstable 
in dry weather. Such roads require very different 
treatment from those on clay or loam. No attempt 
should be made to round up the road, as it is an advan- 
tage to retain as much moisture as possible. If clay 
is available, it is desirable to mix clay with sand in 
the road surface. If clay is put upon the surface when 
the materials are damp, the traffic will mix them 
thoroughly together and the surface will become hard 
when it dries out, and make a good road surface. It is 
only necessary to keep the surface smooth while it 
is drying. 

As a general thing, unless a sand road can be resur- 
faced, it is better to avoid disturbing it, and the less 
work done upon it the better. If there is but little 
travel over it, sod and weeds may grow in the sand, 
and these should not be eradicated. 



IMPROVEMENT OF COUNTRY ROADS. 93 

Art. 28. Gravel Roads. 

In the improvement of a country road, where the 
construction of a good Telford or macadam road can- 
hot be undertaken, a surface of gravel may frequently 
be used to advantage, giving much better results than 
could be obtained with the surface of earth. Even 
a light layer of gravel may frequently prove of very 
great benefit. 

Where the subsoil is of a porous nature and well 
drained, a layer of three or four inches of gravel, or 
sometimes even less, well compacted, will constitute 
a very considerable improvement, especially if, as is 
usual with these light soils, the nature of the mate- 
rial of the road-bed is particularly unsuitable for the 
wearing-surface, difficult to compact sufficiently to 
shed water, and likely to become soft when wet. 

Gravel for use on 'roads should be of hard, tough 
material, capable of resisting the abrasion of traffic. 
Natural gravels may differ widely in the character of 
the materials composing them, and in many instances 
are harder and more durable than the native stone of 
the same locality. Nearly any gravel will be an 
improvement upon an ordinary road surface, but 
where an important road is being improved the material 
should be carefully selected. The size of pebbles 
composing the gravel is important in considering its 
value for road purposes. As a general thing they 
should not be more than I inch, or at most I J inches, 
in greatest dimension. The size should not be too 
uniform, but the gravel should contain enough small 
fragments to fill the interstices between the larger 
pieces, in order that it may pack well in the road. 
When the gravel is too fine or too uniform, it will not 



94 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

bond properly, and will be difficult to compact into a 
hard surface. The proper gradation of sizes is the 
most important characteristic of good gravel. The 
larger pieces are usually the hardest and most durable 
part of the gravel. They have resisted the grinding 
action which has reduced the other material to smaller 
fragments. It is desirable therefore that there be 
only enough fine material to fill the interstices in that 
of larger size. When fine material is in considerable 
excess the gravel should be screened in order to get the 
best results. In many instances, it is possible to 
greatly improve the quality of gravel by screening 
into two or three sizes and then recombining these in 
proper proportions to produce the most dense material. 

Binder. In order to bind well in the road surface, 
the small spaces between the fragments of gravel must 
be filled with fine material. Without this the frag- 
ments composing the gravel will roll upon each other 
and not pack well. Natural gravel may contain 
enough fine material or soft material which will crush 
under the loads coming upon it to cause it to bind 
well in the road; or it may be necessary to add some 
material to the gravel surface to act as a binder. 
Clay, loam, or stone screenings may be used as a binder. 
It is desirable to use as little binder as is consistent 
with the proper bonding of the gravel. When in excess 
it has a tendency to cause the road to soften in wet 
weather and to crack in dry weather. This is espe- 
cially noticeable with clay binder. If gravel contains 
too much fine material, or when the fine material is 
unevenly distributed through the gravel, it should be 
passed over a one half inch screen, and the fine part 
thus removed be used on the surface as a binder. 

When gravel contains considerable large material, 



IMPROVEMENT OF COUNTRY ROADS. 95 

a screen of 1} to 1^ inches mesh may be used to remove 
such material from the portion of the gravel to be used 
in the surface layer of the road. If the road is to be 
sufficiently thick to be constructed in two layers, 
the larger pebbles screened from the gravel will be 
suitable for use in the lower course. 

Construction. In the construction of a road with 
gravel surface the road-bed should first be brought to 
the proper grade, with a form of cross section the same 
as that to be given the finished road. The gravel is 
then placed upon it and rolled to a surface, or left to 
be compacted by the traffic. It is always advantageous 
when possible to compact the road by rolling. The 
road-bed should be well rolled before placing the 
gravel, and the gravel surface afterward. A smooth 
hard surface may thus be produced, upon which the 
wheels of loaded vehicles may roll without producing 
any visible impression. 

In preparing a road-bed for gravel surface, when a 
light coating of gravel is to be used, the surface of the 
ground is shaped up with the grader in the ordinary 
manner, but using a section natter than the finished 
road is to have. The gravel is then placed and spread 
so as to have the proper thickness at the middle and 
diminish the thin edges at the sides of the road. On 
a good well drained road-bed, this construction with 
gravel four or five inches thick at the middle of the 
road may make a very good country road. Good 
drainage is, however, essential to success with such a 
road. 

On important roads gravel is often used instead of 
broken stone, in the manner described in Chapter V. 
In many localities, gravel exists which is superior in 
hardness and durability to the local stone available 



0,6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

for road metal. In such instances gravel is often 
used for surfacing a stone road. 

Maintenance. A new gravel road when first opened 
to travel may require considerable attention to keep 
it in good condition. The surface should be watched 
and all ruts or depressions which may form be at once 
filled up. When new material must be added in 
repairing a gravel surface, it should be fine and contain 
more binding material than the gravel used in the 
first construction of the road. 

After a gravel* road is thoroughly compacted by the 
traffic, less attention is required to keep it in surface 
until it is worn thin enough to require resurfacing. 

Art. 29. Oiled Roads. 

The use of oil for hardening the surfaces of earth 
and gravel roads originated in California, where it 
has rapidly extended into common practice. The use 
of oil was at first intended only for the purpose of 
laying the dust, and the surface of the road was 
sprinkled two or three times during the summer with 
a light coating of oil. The effect of the oil upon the 
road was such as to very quickly modify both the 
purpose and the method of the application, and many 
roads were soon constructed in which oil was used for 
the purpose of binding together the material of the 
road surface, and thus forming a crust over the road 
which would take the wear of traffic. The results in 
general were satisfactory, giving, in many instances, 
smooth firm road surfaces, free from dust during the 
summer, and without mud in winter. 

Methods of Construction. Several methods have been 
employed in the construction of oiled roads. In the 



IMPROVEMENT OF COUNTRY ROADS. 97 

earlier construction, the oil was applied to the road 
when hard and smooth, the surface being sprinkled 
with the oil, which was absorbed into the surface. 
The following extract from a paper by T. F. White, 
in Engineering Record for Feb. 22, 1902, explains this 
method as commonly practiced: 

"Oil on roads, besides aiding to make a wearing 
surface, preserves the road-bed. It follows therefore, 
that the road-bed should be carefully prepared, well 
graded and shaped, and the surface smoothed and 
packed as firmly as the material of which it is composed 
will permit before the oil is applied. We therefore do 
our grading during the early part of winter, that the 
road-bed may have the benefit of the winter rains, 
and become packed from travel as well as from thor- 
ough rolling. We roll after it has become moistened 
through. Then in the spring, while still moist, we go 
over it with a blade grader or smoother or both, and 
dress up the surface, crowning it as desired; and as 
soon thereafter as the surface is dry and the weather 
is settled and warm, the oil is applied, as much in 
quantity as the material will absorb and mix with. 
This has reference to a road never oiled before. 

"It may be desired to put oil on a road that is not 
in very good shape as to grade and smoothness of 
surface. It is not recommended to apply oil to such 
a road, but circumstances may make it seem desirable. 
In such a road there may be chuck holes full of dust. 
To oil it we go over the holes first, scraping out the dust, 
filling them nearly full of oil, and then with hoe and 
rake, work in the dust, together with sharp sand and 
fine gravel, which are thrown in from a wagon drawn 
alongside, until the holes are filled from bottom up 
with oil, dirt, and gravel, thoroughly mixed together. 



98 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

When all the holes are filled, we apply a coat of oil to 
the whole surface of the road. Should the road be 
very uneven, however, and full of holes, we prefer to 
haul on gravel, of a kind that will pack, and fill up the 
holes and uneven places, saturate with water and roll 
before applying oil. Should the surface of a road be 
worked up to a considerable depth of dust, if it is of a 
nature to pack with water and compression, we drench 
it thoroughly and roll. But if it will not so pack, 
being of too sandy a nature, we pour on the oil, 
attempting to saturate all loose material to the firmer 
stratum below. The only rule we have as to quantity 
of oil to be applied is to put on sufficient to saturate 
all of the loose covering of the road, and secure some 
penetration into the firm road-bed beneath. 

"After the oil is put on in any of these instances 
some appliance for mixing the oil and loose road 
materials is run over the surface backwards and for- 
wards until a thorough mixing is accomplished. If 
the road surface is very loose, a common steel lever 
harrow, with the teeth slanted back, is useful. This 
may be dragged to and fro longitudinally along the 
road, and back and forth spirally across the road, 
until a thorough mixing is secured. On firmer roads 
and where there is little loose covering, a lighter 
implement, with numerous dragging fingers suspended 
from an axle, is better. 

"All this has reference mainly to roads that have 
never been oiled before. When it comes to oiling a 
road the second, third, and later seasons, the operation 
is somewhat different. Should the oiled surface be 
cut through and chuck holes formed (but there will 
be very few holes if the road has been properly looked 
after) , we go over these in the manner • previously 



IMPROVEMENT OF COUNTRY ROADS. 99 

noted for repairing chuck holes, and then apply a 
dressing of oil to the whole surface, just enough 
to saturate the loose material and secure a very slight 
penetration into the old oiled surface. Here I will 
call attention to a danger we may fall into, that of 
putting too much oil on the smooth, hard oiled surface 
we have previously obtained, softening it, and putting 
it in condition to rut, especially under heavy loads. 
We may in this way lose a part of the results of the 
previous year's work. I made this mistake on a road 
last summer, so can speak from experience. But 
enough oil should be put on to cover the entire surface 
as with a thin sheet. Then there will be a surplus of 
oil, and the road, if left without further attention, 
would be sticky and very unpleasant to travel over 
for a considerable time after the application. We 
therefore follow this application on smooth hard roads 
that have previously been oiled, with a sprinkling of 
sand, using fine gravel and sharp sand, such as builders 
use in their mortars. This takes up the surplus oil 
and adds to the wearing surface, and renders the road 
at once comfortable to travel over. The sand soon 
becomes incorporated with the rest of the road material 
and packs down smooth and hard. The quantity of 
sand put on is just sufficient to take up the surplus 
oil and no more. 

"We frequently use this sanding process also when 
applying oil for the first time to a hard smooth road. 
We have used it on a macadamized road in which the 
surface was too tight to absorb the oil, and obtained 
excellent results. It is useful also where oil is applied 
to a tight adobe or other clay road. With the oil and 
sand a wearing surface may be built up on the clay 
and be made to last, while without the sand the oil 



IOO A TEXT-BOOK ON ROADS AND PAVEMENTS. 

has a tendency to ball up with the clay dust and carry 
off. " 

Oil applied to a road surface in this manner is ab- 
sorbed by the material of the road covering to a small 
depth, varying, according to the character of the 
material, from about one half inch to I J inches. This 
forms a thin coating of oiled material over the surface 
of the road, which prevents the formation of dust and 
assists in preventing water from penetrating into the 
road when rain comes upon it. 

In order to secure a greater penetration of oil, in 
some localities, the soil of the road is loosened by the 
use of a harrow to a depth of about two inches, before 
the application of the oil, and is then mixed thoroughly 
by harrowing again before being compacted by the 
roller. The method of application varies with the 
character of the soil, hard soil needing to be loosened 
and harrowed, or to have a coating of sand added, 
while sandy soils may be oiled without being disturbed. 

In oiling a road for the first time, two applications 
of oil are usually made, the second application being 
made at from one week to three months after the first 
one. In most instances the second application of oil 
is accompanied by a thin coating of sand or fine 
gravel, which takes up the surplus oil and forms the 
wearing surface of the road. 

Oil. The oil used for road improvement is commonly 
crude asphaltic petroleum, with specific gravity II 
to 14 degrees, Baume, and containing from 30 to 60 
per cent of "D" grade asphalt. In the earlier work 
the oil was always applied hot, at temperatures from 
150 to 250 degrees Fahr. In later practice cold oil 
has frequently been used and each method has its 
advocates. 



IMPROVEMENT OF COUNTRY ROADS. IOI 

The amount of oil required varies with the charac- 
ter of the soil and the method of treatment. As 
much should be used as the soil will take up. The 
proper amount can only be judged by experience with 
the soil to be treated. The quantity of oil used varies 
from about one-half gallon to I J gallons per square 
yard of road surface for the first application, and 
one-half to I gallon for the second application. The 
maintenance of the roads usually requires an applica- 
tion of oil each spring, the quantit}" required decreas- 
ing from 3 r ear to year. 

PETROLITHIC PAVEMENT. 

The ordinary oiled road consists of a light covering 
of oiled soil upon the road surface. In some instances 
oiled surfaces are made 4 to 6 inches deep, by loosen- 
ing the soil, saturating with oil, and then compacting 
by rolling to a firm surface. Difficulty has been found 
in compacting so deep a layer of oiled earth, and this 
has led to the invention of the petrolithic rolling 
tamper for this purpose. The rolling tamper is shown 
in Fig. 20. It consists of a heavy roller with a large 
number of tampers, or feet, projecting from its surface. 
These feet pack the material, beginning at the bottom, 
and thus compress the whole layer to uniform density. 
An oiled road constructed with this machine is called 
a petrolithic pavement. The following specifications 
used in Los Angeles for this class of streets illustrate 
the method of construction employed in such work: 

"After the street has been brought to the required 
grade and cross-section as above specified, the sur- 
face shall be rolled with a roller weighing not less than 
250 pounds to the inch width of tire until the surface 



102 A TEXT -BOOK ON ROADS AND PAVEMENTS 

is unyielding. Depressions made by the rolling shall 
be leveled up with good earth and again rolled. Such 




Fig. 20. 

portions of the street as cannot be reached by the 
roller, and all places excavated below grade and 
refilled, and all pipe trenches and other places that 
cannot be properly compacted by the roller, shall be 
tamped solid, and in case of wet weather or soft or 
muddy ground, making use of the roller unsafe or 
impracticable, the rolling shall not be undertaken until 
the ground has become sufficiently dry. 

" The street shall then be tested for grade and cross- 
section, and no further work shall be done upon it 
until a certificate shall have been issued stating that 
it is acceptable in these respects. It shall then be 
plowed to a depth of not less than six inches and 
thoroughly pulverized by cultivating and harrowing. 



OILING. 



Oil shall then be applied as follows: 

The area to be oiled shall extend from curb to curb 



IMPROVEMENT OF COUNTRY ROADS. 103 

where there are no gutters, and where there are gutters 
then from gutter to gutter, including all intersections 
of streets and alleys, and to the property line on both 
sides of said intersections. 

"The roadway shall be coated evenly with the oil 
at the rate of one gallon to the square yard of surface 
covered. It shall then be thoroughly cultivated to a 
depth of 4 inches until the oil is well mixed with 
the soil. A second application of oil, at the rate of 
one gallon to the square yard of surface covered, shall 
then be made and the area shall be again cultivated 
to a depth of 4 inches until the oil and soil are well 
mixed. The street shall then be plowed 4 inches deep 
with a plow that thoroughly turns over the furrows. 

" A third application of oil, to the extent of one gallon 
per square yard of surface covered, shall then be made, 
and the 'entire surface shall be thoroughly cultivated 
to a depth of 6 inches, a portion of the cultivating 
being done along diagonal lines so as to thoroughly 
mix the surface. The road-bed shall then be tamped 
with the tamping roller until it is solid to within 3 
inches of the finished surface. It shall then be graded 
with a road grader until it substantially conforms to 
the official cross-section, and shall then be tamped with 
the tamping roller until the entire surface is uniformly 
hard, solid and free from undulations or other irregu- 
larities. 

" The completed surface of the street must conform 
substantially to the established grade and cross- 
section. Should it be low, it shall be broken up to 
a depth of at least 2 inches, fresh earth and oil supplied 
and the surface again rolled as before. 

"Should an excess of oil remain upon the surface 
after it has been thoroughly completed, such oily 



104 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

portion shall be plowed to a depth of at least 6 inches 
and retamped. 

" In the process of cultivating, the surface shall be 
gone over not less than twice after each of the first two 
applications of oil, and not less than three times after 
the third application, and in all cases until the oil and 
soil are thoroughly mixed. 

" The total quantity of oil to be applied on the street 
shall be not less than three (3) gallons net oil by 
measure for every square yard of surface covered. 

"At all stages of the work sufficient water shall be 
applied to secure the best results in the tamping, the 
amount of water to be used to be governed by the 
character of the soil, the intention being to make 
the soil just damp enough to pack solid. 

"Any portion of the street that cannot be reached 
by the roller shall be tamped solid by hand, under the 
direction of the Board of Public Works. 

" The contractor will be held responsible for all 
damage to curbs, gutters, or cross-walks that may be 
caused by him in the performance of the work. 

OIL. 

"The oil used shall be crude petroleum and shall 
conform to the following requirements: 

" (a) Specific Gravity : The oil, after being freed from 
water and sediment, shall be of not less than eleven 
and five-tenths (11.5) degrees, and not more than 
fourteen (14) degrees, Baume, gravity, at sixty (60) 
degrees F. 

" The specific gravity shall be determined by the use 
of 'The Westphal Specific Gravity Balance/ in con- 
junction with the accepted scale hereinafter described 



IMPROVEMENT OF COUNTRY ROADS 105 

for addition and deduction below or above normal 
temperature. 

"(b) Temperature: All oil must be delivered at the 
point required for sprinkling at a temperature of not 
less than one hundred (100) degrees nor more than one 
hundred and ninety (190) degrees F. 

"(c) Measurement: In determining the quantity of 
oil delivered, the correction for expansion by heat shall 
be as follows: From the measured volume of all oil 
received at any temperature above 6o° F., an amount 
equivalent to 0.4 of one per cent for every io° F. shall 
be subtracted as the correction for expansion by heat. 
For the purpose of measuring oil a temperature of 
6o° F. shall be deemed normal temperature. 

"(d) Volatility: The oil shall not contain more than 
eight (8) per cent of matter volatile when said oil is 
heated slowly to two hundred and twenty (220) degrees 
F. and maintained at that temperature during fifteen 
(15) minutes. 

"(e) Asphalt: The oil shall contain not less than 
sixty (60) per cent of asphalt, having at a temperature 
of seventy-seven (77) degrees F. a penetration of eighty 
(80) degrees, District of Columbia Standard. 

" The percentage of asphalt shall be determined, using 
oil treated as described in Section (d) in the following 
manner: A weighed amount of said treated oil shall be 
heated, in an evaporating oven, to a temperature of 
four hundred (400) degrees F. until it has reached the 
proper consistency, when the weight of the residue 
shall be determined and the per cent calculated. 

" (f) Water and Sediment: Deduction will be made 
for water and sediment in exact proportion to the 
percentage of such water and sediment found therein, 
and the oil shall not contain over two (2) per cent of 



106 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

such water and sediment as determined by the gasoline 
test. 

"(g) Tank Wagons : All tank wagons used for deliver- 
ing the oil must first be submitted to the Department 
of Oil Inspection, which will gauge and stamp into the 
steel heads of said tanks the capacity in gallons of said 
tanks, and no figures of capacity will be accepted other 
than the official rating given by the Department of Oil 
Inspection. 

" (h) All oil to be used shall be tested by the Depart- 
ment of Oil Inspection. 

ROLLER. 

"The tamping roller to be used in the execution of 
the work herein specified shall consist of a roller the 
outer surface of which shall be studded with teeth not 
less than 7 inches long and having a surface area of not 
less than 4 square inches each, the roller itself to be of 
such a weight that the load upon each tooth shall be 
not less than 300 pounds/' 

Results of the Use of Oil on Roads. As already stated, 
good results seem to have been obtained in California 
with the use of oil both for laying dust on roads and 
for improving the resistance to wear and to the pene- 
tration of water into the road surface. The results 
obtained depend upon the character of the work and 
the care used in construction. To secure good results 
these roads require careful maintenance. The forma- 
tion of chuck holes due to the action of water upon the 
road is a principal difficulty, and these require prompt 
repair. A lightly oiled road surface is worn away by 
travel and water during the rainy season, and must 
be annually renewed. On the whole the results are 



IMPROVEMENT OF COUNTRY ROADS. lO? 

reported as satisfactory and the use of oil is largely 
extending. 

California has a dry climate, which is very favorable 
to this kind of construction. The object of the road 
improvement is rather to get rid of the dust, and cause 
the surface of the roads to hold together during the 
dry season, than to guard against the softening of the 
roads in wet weather. Under these conditions the use 
of oil constitutes a very desirable method of road 
improvement; while the occurrence of the asphaltic 
oil, which may be obtained at low cost, makes possible 
economical construction. 

In considering the advisability of extending such 
methods to other parts of the country, the differences 
of climate and of the purpose of road improvement 
should be taken into account, as well as the character 
of available materials. Some method of dealing with 
dust, other than that of sprinkling with water, is 
annually growing more important, while the breaking 
up, or raveling, of road surfaces during dry weather 
is a serious difficulty, particularly where there is con- 
siderable automobile travel. The parafhne oils of the 
Eastern states may act quite differently from the 
California asphaltic oils, while the greater amount of 
rainfall and differences in temperature will probably 
make oiled construction much more difficult to 
maintain in other parts of the country than in 
California. 

For California the value of these materials has been 
fully demonstrated, although experience is likely to 
modify the methods of construction used. For other 
localities, the value both of materials and methods 
can be determined only by experiment. 



108 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 30. Sand-Clay Roads. 

In some of the Southern states where other materials 
for surfacing roads are not available, a mixture of sand 
and clay in proper proportions has been found a desir- 
able material for this purpose. In some instances 
the mixing of sand and clay for road work has received 
considerable attention, and good results have been 
obtained. The relative amounts of sand and clay to 
be used depend upon the character of the materials 
and can only be determined by experiment in each case. 
Where good materials are available, a fairly hard 
surface, well adapted to light traffic, may be obtained. 
It is claimed that these roads are less noisy and less 
dusty than macadam. They require the same main- 
tenance as an ordinary earth road, but form a harder 
surface than earth usually found in a natural state. 
Mr. William L. Spoon, of the United States Office of 
Public Roads, has made an investigation and report 
upon this method of construction. 

* " The best sand-clay road is one in which the wear- 
ing surface is composed of grains of sand in contact in 
such a way that the voids or angular spaces between 
the grains are entirely filled with clay, which acts as a 
binder. Any excess of clay above the amount necessary 
to fill the voids in the sand is detrimental. If a small 
section taken from the surface of any well constructed 
sand-clay road is examined with a magnifying glass, 
the condition of contact which exists between the 
grains of sand and the small proportion of clay which 
is required to fill the voids may be seen. Wherever 
this proper condition of contact exists for a few inches 

* U. S. Department of Agriculture, Office of Public Roads, Bulletin 
No. 27. 



IMPROVEMENT OF COUNTRY ROADS. IO9 

in thickness upon the surface of the road, it will bear 
comparatively heavy traffic for a long time, even when 
the subsoil is sand or clay. 

" All the experiments which have been made by this 
Office indicate that the materials should not be mixed 
in a dry state, but that they should be thoroughly 
mixed and puddled with water. It makes little 
difference by what method the stirring or mixing is 
done, so long as it is thorough and proper proportions 
of the materials are obtained. If an excess of clay is 
used in the mixture, the grains of sand which are not in 
contact are free to move among and upon each other, so 
that no particle exerts more resistance to pressure than 
if the entire mass consisted of clay alone. On the other 
hand, if an insufficient amount of clay is used, the mix- 
ture will lack binding power and will soon disintegrate. 

" It has been pointed out that thorough stirring and 
puddling are absolutely essential to successful sand- 
clay construction. This is most easily brought about 
immediately after a hard or prolonged rain, the clay 
having been previously spread and the large lumps 
broken up as completely as possible. The surface 
should then be covered with a few inches of sand and 
plowed and harrowed thoroughly by means of a turning 
plow and a cutaway or disk harrow. This stage of 
the work will of course be found somewhat disagree- 
able, leading, as it does, to the formation of a thick, 
pasty mud; but it is the only practicable way in which 
the necessary mixing can be accomplished. Many 
experiments have been tried with dry mixing of the 
clay and sand, but all have been more or less unsuccess- 
ful. In cases where the plowing and harrowing are 
considered too expensive, the mixing may be left to 
traffic. This, however, inevitably leads to a muddy 



110 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

road surface for a long time, although finally it is 
possible, by a proper distribution of the sand upon the 
clay, to bring about a fairly good result, even by this 
simple method." 

" It has already been shown that the best mixture for 
sand-clay construction is one in which there is just 
enough clay to fill the void in the sand, thus producing 
the proper cementing bond in the road surface. No 
exact rules can be laid down for calculating in advance 
the best mixture. It must be remembered that the 
relation of weight and volume will vary widely in 
different clays, according to the amount of water which 
they contain. Some clays, especially the more plastic 
varieties, even after they are as thoroughly dried as 
they can be by the hottest summer sun, will still hold 
as much as 20 per cent of water. This water is known 
to chemists as 'water of combination/ because it 
seems to be either combined with or held in the structure 
of the clay particles in such a way that it can only be 
driven out at a high temperature. It is apparent from 
this that in handling a clay of this kind, even when it 
seems quite dry, each ton will contain 400 pounds of 
water which does not enter into the consideration of 
volume. The amount of clay necessary to fill the voids 
in any given sand will therefore be found to vary." 

"Practical experience has shown that the tendency 
is to calculate too little rather than too much sand for 
given amounts of clay, and almost invariably a second 
and even a third application of sand is necessary over 
and above the calculated amount. It often happens 
that clay will work up to the surface under the action of 
traffic, in which case an extra top dressing of sand 
should be added when required. " 

Upon a clay subsoil "the foundation having been 



IMPROVEMENT OF COUNTRY ROADS. Ill 

properly prepared, the surface should be plowed and 
harrowed to a depth of about 4 inches until it is pul- 
verized as completely as possible. It is then covered 
with 6 to 8 inches of clean angular sand. The sand 
should be spread so that the layer is thickest at the 
center of the road, following in general the same method 
as was outlined for spreading clay upon a sandy founda- 
tion. The first mixing by plow and harrow is now 
done while the materials are still in a comparatively 
dry state. It has been found that the clay founda- 
tion can be more evenly disintegrated when in that 
condition. After this first mixing has been finished 
the road is finally puddled with a harrow after a rain. 
In case an excess of clay works to the surface and tends 
to make the mixture sticky, sand is applied until this 
trouble is overcome. 

"Upon the completion of the mixing and puddling, 
the road should be shaped while it is still soft enough 
to be properly finished with a scraper and at the same 
time stiff enough to pack well under the roller or under 
the action of traffic. In case it is impossible to obtain 
,the proper consistency of the surface material, it is 
better to shape the road when somewhat too wet than 
when it is too dry, even if it is necessary to stop traffic 
upon it for a few days. The road should be opened to 
traffic as soon as practicable after completion, as this 
will be found to have a beneficial effect upon it." 

Art. 31. Miscellaneous Roads. 

Corduroy Roads. In timbered country, where roads 
must pass over wet and muddy places, corduroy roads 
are sometimes employed. They are built by laying 
logs side by side across the roadway. By taking 



112 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

sufficient care in construction to select the logs and 
even up the spaces between them with smaller pieces, 
a reasonably smooth road may be built. Roads of 
this kind are at best very rough affairs, and require a 
great deal of work to keep them in fair condition for 
travel. They are of value only as temporary roads 
across bad places where the cost of a better road would 
be too great. 

Plank Roads. Many of the old toll roads in some 
parts of the country were plank roads, and at one time 
they were quite common. They are now rarely con- 
structed. The road is built of planks 2 to 4 inches 
thick and 8 or 9 feet long, laid upon two rows of stringers 
about 5 feet apart. The ends of the planks are not in 
line but are stepped off to assist wagons in passing from 
the side upon them. Usually a single line was used and 
teams turned out upon the earth road at the side in 
passing; but sometimes a double track was provided 
for teams in each direction. When in good condition, 
roads of this kind may be very good for travel, but they 
very quickly get out of repair and are not economical. 

Shell roads. In some localities where oyster shells 
are plentiful, these are used in constructing roads. 
They make a road very similar to that built of a soft 
limestone. The road is constructed in the same 
manner as with gravel, the shells being readily com- 
pacted by the traffic, and binding well in the road. The 
material is too soft to resist the wear of heavy traffic, 
and grinds up rapidly under travel. For localities 
where traffic is not heavy and a harder road covering 
would be expensive, these roads have often been found 
satisfactory and economical. 

Burnt-Clay Roads. In certain districts in the 
Southern states, sedimentary clays very commonly 



IMPROVEMENT OF COUNTRY ROADS. II3 

occur, and other road materials are not available. It 
has been proposed to form a road surface by burning 
the clay, and experiments have been made by the 
United States Office of Public Roads which seem to 
indicate that in many instances this may prove an 
effective means of road improvement in such localities. 

* " After grading the road to an even width between 
ditches, it is plowed up as deeply as practicable. It 
will be found necessary to use four horses or mules, as 
the extremely heavy nature of the clay makes the work 
of deep plowing difficult. After the plowing has been 
completed, furrows are dug across the road from ditch 
to ditch, extending through and beyond the width to 
be burned. If it is intended to burn 12 feet of roadway, 
the transverse furrows should be 16 feet long, so as to 
extend 2 feet on each side beyond the width of the final 
roadway. Across the ridges formed by these furrows — 
which should be about 4 feet apart — the first course 
of cord wood is laid longitudinally so as to form a 
series of flues in which the firing is started. From 15 
to 20 of these flues are fired at one time. 

"The best and soundest cord wood is selected for 
this course and should be laid so that the pieces will 
touch, thus forming a floor. Another layer of wood is 
thrown irregularly across this floor, in crib formation, 
with spaces left between in which the lumps of clay 
are piled. Care should be taken that the clay placed 
on this cribbed floor is in lumps coarse enough to allow 
a draft for easy combustion. 

" After the lumps of clay have been heaped upon this 
floor, another course of wood is laid parallel to the 
first. The third layer is laid in exactly the same manner 

* U. S. Department of Agriculture, Office of Public Roads, Bulletin 

No. 27. 



114 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

as the first, and each opening and crack should be 
filled with brush, chips, bark, small sticks, or any other 
combustible material. The top layer of clay is placed 
over all and the finer portions of the material are heaped 
over the whole structure. A careful arrangement of 
this cord wood cribbing to separate the clay is impor- 
tant, and the directions should be carefully followed. 

"The deep covering of clay which is thrown over all 
should be taken from the side ditches, and may be in 
lumps of all sizes, including the very finest material. 
It is spread as evenly as possible over the top in a 
layer of not less than 6 to 8 inches. Finally the 
whole is tamped and rounded off so that the heat will 
be held within the flues as long as possible. When 
coal slack is available the two top layers of wood 
may be omitted and the coal slack thoroughly mixed 
with the clay. 

"It is necessary to get the fires in the flues well 
under way before the first layer of wood is burned 
through. The first action of the fire is to drive out 
the water contained in the clay before the actual burn- 
ing and clinkering % can begin. In burning the gumbo 
clays a great advantage is gained from the organic and 
vegetable matter which is contained in the clay, as 
that in itself aids combustion. " 

"After the firing is completed not only the portion 
of the clay which forms the top of the kiln but the 
ridges between the flues should be burned thoroughly, 
so as to form a covering of burnt clay 10 to 12 inches 
in depth, which, when rolled down and compacted, 
forms a road surface of from 6 to 8 inches in thickness. 
If properly burned, the material should be entirely 
changed in character, and when it is wet it should have 
no tendency to form mud. 



IMPROVEMENT OF COUNTRY ROADS. 1 15 

"When the material is sufficiently cooled the road- 
bed should be brought to a high crown before rolling, 
in order to allow for the compacting of the material. 
This can best be done with a road grader. After this 
the rolling should be begun and continued until the 
road-bed is smooth and hard. The finished crown 
should have a slope of at least one-half inch to the 
foot. " 

Slag Roads. Blast furnace slag is used in some 
localities as a material for surfacing roads. In some 
instances also slack from coal mines is used in the same 
way. Where these materials are available, they may 
provide a cheap method of improving the surfaces of 
roads of light traffic. Usually these materials are 
rapidly reduced to powder under any considerable 
traffic; in some instances, however, slag may be ob- 
tained which is hard and tough and forms a desirable 
road metal. 

Art. 32. Width of Tires. 

The effect of the width of wheel tires upon the 
resistance to traction has already been mentioned in 
Art. 2. For ordinary roads, not in soft condition, 
tractive resistance is somewhat less for wide than for 
narrow tires. This difference, while not usually very 
great, is sufficient to be quite appreciable in the work 
of hauling heavy loads upon the roads. Narrow tires 
have a much more destructive effect upon a road 
surface than wide ones, and from the point of view 
of road maintenance, wide tires are very desirable. 
The concentration of a heavy load upon narrow wheel 
tires affords very little surface of contact between 
the wheel and road, and causes the wheel to indent the 
road surface, giving a powerful cutting action. The 



Il6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

same load on a tire of sufficient width would tend to 
compact the road, acting like a roller, and if these 
wheels are so placed as not to run in the same track, 
the difference would be still more marked. There is, 
however, no advantage in an excessive width of tire. 
When this exceeds 4 or 5 inches, upon a properly 
crowned road, the tire will be only partially in contact 
with the road and the load will be carried on one edge 
of the tire, which will indent the road surface. 

The general introduction of wide tires upon vehicles 
traveling our highways would greatly simplify the 
problem of road maintenance, particularly upon earth 
roads. This fact is generally admitted and appre- 
ciated by road builders, but the practical difficulties 
met in attempting to change the prevailing system 
of narrow tires has been too great, and the agitation 
for wide tires has not as yet produced much effect. 
Many propositions have been made looking toward 
the regulation of the width of tires by law. This has 
not met with much success. In some states the laws 
provide for a rebate upon road taxes to persons using 
wide tires upon wagon wheels used for highway 
transportation. 

The usual width of tire upon ordinary wagons is 
I J or if inches. For the best effect upon the high- 
ways, these should be increased so as to vary from 
about 3 to 5 or 6 inches, according to the load for 
which the wagon is designed. 

The wide tire is at a disadvantage on a distinctly 
bad road, and efforts to secure the adoption of wider 
tires can hardly meet with much success until very 
great improvement has taken place in the character 
of the country roads. Wider tires should naturally 
follow better roads and assist in maintaining them. 



CHAPTER V. 
BROKEN-STONE ROADS. 
Art. S3- Definition. 

Broken-stone roads consist essentially of a mass of 
angular fragments of rock deposited, usually in layers, 
upon the road-bed or a foundation prepared for it, and 
then consolidated to a smooth and uniform surface by 
means of a roller or by the action of the traffic which 
passes over it. 

There are two commonly recognized systems of con- 
structing broken-stone roads, differing in the nature of 
the foundation employed, and known respectively by 
the names of the men who first introduced them into 
English practice as Telford roads and Macadam roads. 

Each of these systems has been greatly modified in 
use since the time of its founder, and each name is now 
used to cover a general class of constructions differing 
very materially within itself as applied in the practice 
of different engineers. Each of the systems also has 
its earnest advocates, who contend for its. exclusive use, 
and numerous controversies have been the result, at 
the conclusion of which each party is "of the same 
opinion still. " The view taken by different road- 
builders in this matter, it may be remarked, appears to 
be the result usually of the local necessities of the 
vicinities in which they work, and of the skill with which 
the different systems have been applied in work which 
has come under their observations. In road-building, 

117 



Il8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

as in any other class of engineering works, no rigid 
rules can be laid down for universal application; each 
road must be designed for the place it is to occupy and 
the work it is to do. 

In some parts of this country natural gravel is sub- 
stituted for broken stone in the construction of these 
roads, the methods of construction being the same as 
in using broken stone. 

Art. 34. Macadam Roads. 

Macadam roads as commonly constructed consist of 
two or more layers of broken stone, each layer being 
rolled to a firm bearing before placing the next. The 
broken stone is usually placed directly upon the earth 
road-bed. 

In constructing a macadamized roadway, the road- 
bed is first brought to the proper grade in the usual 
manner, and rolled to a uniform surface. The surface 
of the road-bed is either flat or raised at the middle to 
the same section as is to be given the finished road- 
surface. The inclined form is usually employed, and 
seems preferable on account of affording better drain- 
age in case any water finds its way through the surface 
layer. 

On village streets where curb and sidewalks are 
employed, this section of the road-bed may extend to 
the curbing (as shown in Fig. 3) , but on country roads a 
bench of earth should be left at the side between the 
broken stone and the gutter in order to confine the 
broken stone while it is being compacted, and prevent 
the spread of the surface materials. The form of the 
road-bed before placing the stone would then be as 
shown in Fig. 21, where the completed road is to be of 



BROKEN-STONE ROADS. 1 1 9 

the form given in Figs. 5 and 17. Where the road-bed 
is in embankment, it is common to construct the earth 
embankment to the height of the finished surface, and 
afterwards excavate the material necessary to admit of 
placing the surface layers. The embankment should 
be allowed to settle and become thoroughly compacted 
before the broken stone is placed upon it, and it is 
desirable with new embankments that they be used for 
a short time by the traffic upon the earth surface be- 

Fig. 21. 

fore finishing the road; where, however, the material 
is well compacted in construction and can be thor- 
oughly rolled this is not necessary. 

In constructing the road-bed its proper drainage 
must be considered, and where necessary to prevent its 
becoming wet under the broken stone some means 
should be adopted to artificially drain it. 

Upon the completion of the road-bed, a layer of 
broken stone, usually from 3 to 5 inches in thickness, is 
placed upon it and thoroughly rolled. Upon this a 
second layer is placed and likewise rolled to a uniform 
surface. Sometimes a third layer is added, or in case 
of a very thin road it may consist of a single layer, the 
number of layers depending upon the thickness of the 
road. When no roller is used, the stone is usually 
spread on the surface of the road-bed to the full thick- 
ness desired for the road, and left to the action of the 
traffic. 

The upper layer constitutes the wearing surface of 
the road, and upon this it is usually necessary to place 



120 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

a thin layer of finer material called binding material, 
which may consist of rock chips, sand, small gravel, or 
sometimes loam, and is washed and rolled into the inter- 
stices of the rock, with the object of forming a com- 
pact and impervious surface. Binding material is in 
like manner often added to the lower layers of the 
road, although this has not been common practice. 
The object should be to fill the voids in the rock as 
completely as possible, serving to make the road one 
solid mass, to bind the rock more firmly together, and 
to prevent the percolation of water through the surface. 

Art. 35. Telford Foundations. 

The distinguishing feature of a telford road is its 
paved foundation. It consists essentially of a pave- 
ment of stone blocks set upon the road-bed and cov- 
ered with one or more layers of broken stone. 

In forming a telford road the road-bed is con- 
structed in the same manner as for macadam, being 
made either level or crowned. A pavement is then 
placed upon the road-bed from 5 to 8 inches thick, de- 
pending upon the thickness to be given the road 
material, the general practice being to make the pave- 
ment about two thirds of the total thickness of the 
road. The stones used for the pavement may vary 
from 2 to 4 inches in thickness and 8 to 12 inches in 
length; they are set upon their widest edges and with 
their greatest lengths across the road. The irregulari- 
ties of the upper part of the pavement are then broken 
off with a hammer, and all the interstices filled with 
stone chips and wedged with a light hammer so as 
to form a completed pavement of about the thickness 
required. 



BROKEN-STONE ROADS. 121 

Upon this pavement the layers of broken stone are 
placed, and the road-surface completed in the same 
manner as for a macadam road. 

The practice of Telford was to grade the road-bed 
flat, and then construct his pavement deeper in the 
middle than at the sides, using for a roadway 1 6 feet 
wide stones about 8 inches deep at the middle and 
5 inches at the sides. This practice is still followed by 
some engineers, but it is now more common and usually 
considered preferable to make the surface of the road- 
bed parallel to the finished surface and the pavement 
of uniform thickness. Fig. 22 shows a section of tel- 
ford road as now commonly constructed. 




Fig. 22. 

The following extract from the specifications of Mr. 
James Owen, for telford roads in Essex County, New 
Jersey, may be regarded as representing the best prac- 
tice in such construction. 

"After the road-bed has been formed and rolled, as 
above specified, and has passed the inspection of the 
Engineer and Supervisor, a bottom course of stone, 

of an average depth of inches, is to be set by 

hand as a close, firm pavement, the stones to be placed 
on their broadest edges lengthwise across the road in 
such manner as to break joints as much as possible, 
the breadth of the upper edge not to exceed four (4) 
inches. The interstices are then to be filled with 
stone chips, firmly wedged by hand with a hammer, 
and projecting points broken off. No stone of greater 



122 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

length than ten (10) inches or width of four (4) inches 
shall be used, except each alternate stone on outer 
edge, which shall be double the length of the others 
and well tied into the bed of the road; all stones with 
a flat smooth surface must be broken, the whole sur- 
face of this pavement to be subject to a thorough 
settling or ramming with heavy sledge hammers, and 

thoroughly rolled with a ton roller. No stone 

larger than one and one-half (ij) inches to be left 
loose on top of telford. ' 

The proper foundation to be used for a broken-stone 
road depends upon the nature and condition of the 
road-bed upon which it is to be constructed and the 
nature of the traffic to pass over it. If a firm, well- 
compacted, and thoroughly drained road-bed may be 
obtained, of material which will not readily soften 
under the action of moisture, there will usually be no 
need for a special foundation, but the first layer of the 
macadam may be placed directly upon the surface of 
the road-bed. If, however, the road-bed is of a ma- 
terial retentive of moisture, not thoroughly drained, 
and likely to become soft in wet weather, and the 
broken stone be laid immediately in contact with it, 
the stones of the lower layer of macadam may be grad- 
ually worked down by the weight of the traffic into the 
soft earth, and the soil at the same time work up into 
the voids in the stone, causing a gradual disintegration 
of the road. It may thus also become retentive of 
moisture and subject to the disrupting action of frost. 
In this case some foundation must be provided which 
is capable of resisting the penetrating action of the soft 
material of the road-bed and of distributing the load 
over it. 

It is not intended in the above to imply that the 



BROKEN-STONE ROADS. 123 

use of a foundation of this character should take the 
place of proper drainage. The advisability of artificial 
drainage should always be carefully considered, and 
where the road is threatened by water which may be 
removed by the construction of drains they should be 
used, but frequently thorough drainage is difficult or 
doubtful, and it is desirable to adopt heavy construc- 
tion such as the telford foundation gives. 

It is commonly claimed by the advocates of the 
macadam system of construction that on any well- 
drained and well-compacted road-bed there will be no 
tendenc}^ on the part of the stone to work down or of 
the soil to work up, and hence that the Telford foun- 
dation is an unnecessary expense. The difficulty of 
procuring a perfectly stable and reliable road-bed in 
many localities is, however, very generally recognized, 
and telford pavements are largely used. 

The Massachusetts Highway Commission has dis- 
continued the use of telford construction. In their 
report for 1903 they give the following as their reasons 
for this course: 

"No telford foundations have been laid for two 
years past. Much of this class of construction has 
been done by the commission, and every contingency 
was supposed to have been carefully considered. 
Notwithstanding the careful attention to details, the 
results from the use of telford have been far from 
satisfactory. In a few cases the large stones have 
come to the surface in a manner which would seem 
to indicate a movement due to frost action. In other 
cases, where a fairly soft native stone was used for 
surfacing, the upper courses were worn away so as 
to leave the large stones exposed. There are few, 
if any, cases where equally good results cannot be 



124 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

obtained by the use of sand, gravel, or small stones 
in place of telford, and at a less cost." 

These difficulties do not seem to have been met by 
other road builders, and where conditions are such as 
to make advisable the construction of thick, heavy 
roads, telford construction is very commonly adopted 
as the cheapest form for such work. 

The Massachusetts Highway Commission has also 
adopted for difficult construction on wet, heavy soils, 
a blind center drain, and consider this cheaper than 
the telford construction. This is described in their 
report for 1904 as follows: 

"On heavy, wet soils a center 'V '-shaped drain 
has been substituted for the side drains and telfording. 
In building this type of road the earth is loosened and 
thrown out toward the sides, so as to give a 'V- 
shaped trench, with its greatest depth in the center 
of the proposed roadway. Narrow trenches are cut 
through the sides of this center trench, at intervals 
of 50 or more feet, connecting its lowest part with the 
gutters on the side, and placed at a depth and slope to 
thoroughly remove all water. The center and cross 
ditches are filled with field or wall stone, the depth 
of this stone varying from 12 to 18 inches at the 
center, and from 6 to 12 inches on the sides, the thick- 
ness being dependent upon the character of the soil 
in the sub-grade. The tops of these large stones are 
given a crown to receive the surfacing material/' 

Art. 36. Rocks for Road Building. 

Properties Required. The surface material for broken- 
stone roads must bind together into a solid surface 
capable of bearing the loads which come upon it and 
of resisting the wear of the traffic. 



BROKEN-STONE ROADS. 12 5 

A stone to be durable in the surface of a road should 
be as hard and tough as possible. The qualities of 
toughness and resistance to abrasion are of more 
importance than hardness and resistance to crushing. 
A stone may be hard and brittle and quickly pound 
to pieces in . a road surface, or it may have a high 
crushing strength and grind away quickly under 
abrasion, as is the case with some varieties of sand- 
stone. If, however, it be too soft, it may crush 
under the loads coming upon it, and thus lack in 
durability. 

A stone for a road-surface must also resist well the 
disintegrating influences of the atmosphere. It should 
be as little absorptive of moisture as possible in order 
that it may not be liable to injury from the action 
of frost. Many limestones are objectionable on this 
account. 

The material of a road-surface should also be uni- 
form in quality; otherwise the wear of the surface will 
not be even, and depressions will appear where the 
softer material has been placed. 

As the under parts of the road are not subject to 
the wear of the traffic, and have only the weight of the 
loads to sustain, it is evidently not important that the 
foundation or lower layers be of so hard or tough a 
material as the surface; and hence it is frequently pos- 
sible, by using an inferior stone for that portion of the 
work, to greatly reduce the cost of construction. 

The binding of the road-surface into a compact mass 
capable of resisting the wear of traffic depends largely 
upon the cementing properties of the material. By 
the cementing power of the stone is meant that 
property which enables the fine dust to act, when wet, 
as a cement and bind the fragments of rock composing 



126 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the road-surface firmly together. This is perhaps the 
most important quality of the material, and a high 
cementing value is always desirable. The tenacity 
with which the fragments of rock are held together is 
perhaps more important in the wear of the road than 
the resistance to wear of the fragments themselves. 
The powdering of the cementing material in dry weather 
sometimes causes the loosening of the stones and the 
raveling of the broken-stone surface. This is more 
apt to occur where the road metal is hard and resistant 
to wear than where it grinds up more rapidly. 

The character of the material which will give the 
best results in a road-surface depends upon the local 
conditions under which the road is to be built and 
the traffic to which it is to be subjected. Under heavy 
traffic, hard and tough road metal is necessary to 
good results. Under lighter traffic, a softer rock may 
sometimes be better if it is coupled with good binding 
properties. 

* "Experience shows that a rock possessing all 
three of the properties mentioned in a high degree 
does not under all conditions make a good road material; 
on the contrary under certain conditions it may be 
altogether unsuitable. As an illustration of this, if 
a country road or city parkway, where only a light 
traffic prevails, were built of a very hard and tough 
rock with a high cementing value, neither the best 
nor, if a softer rock were available, the cheapest results 
would be obtained. Such a rock would so effectively 
resist the wear of a light traffic that the amount of 
fine dust worn off would be carried away by wind and 
rain faster than it would be supplied by wear. Conse- 
quently the binder supplied by wear would be insuffi- 
* Engineering Record, May 17, 1902. 



BROKEN-STONE ROADS. \2J 

cient, and if not supplied from some other source the 
road would soon go to pieces. The first cost of such 
a rock would in most instances be greater than that of 
a softer one, and the necessary repairs resulting from 
its use would also be very expensive/' 

The selection of material for road metal is commonly 
determined rather by the cheapness and convenience 
of location than by its desirability for the purpose. In 
most instances this is of necessity the case, and the 
availability of material in vicinity of the work makes 
possible the construction of the road. It is, however, 
frequently possible, by judicious selection of materials, 
to greatly improve the results obtained in such work, 
and while the selection of a stone for road construction 
will of course always depend largely upon what is to 
be obtained in the locality of the work, the importance 
of a thoroughly good material in the road surface is 
so great in its effect upon the durability and cost of 
repairs of the road that it may frequently be found 
economical, on roads subjected to a considerable traffic, 
to bring a good material a considerable distance rather 
than to use an inferior one from the immediate vicinity. 
It may also be suggested in this connection that in 
many instances railway transportation over a consid- 
erable distance may be small compared with wagon 
transportation over a short distance, and the impor- 
tation of good material may add but slightly to the 
aggregate cost of the work. 

Classification. The rocks used for road-building 
differ widely in their mineral characters. The classifi- 
cation shown in the following table is proposed by 
Mr. Edwin C. E. Lord.* 

* U. S. Department of Agriculture, Office of Public Roads, 
Bulletin No. 31. 1907. 



128 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



GENERAL CLASSIFICATION OF ROCKS. 



I. Igneous. 



Intrusive (plutonic) ' 



II. Sedimentary. 



2. Extrusive (volcanic) 



i. Calcareous. 



a. Granite. 

b. Syenite. 

c. Diorite. 

d. Gabbro. 

Peridotite. 

Rhyolite. 

Trachyte. 

Andesite. 

Basalt and diabase. 
Limestone. 
Dolomite. 



III. Metamorphic. 



I a. Shale, 

b. Sandstone, 

c. Chert (flint). 

!a. Gneiss." 

b. Schist, 

c. Amphibolite. 

{a. Slate, 

b. Quartzite. 

c. Eclogite. 

d. Marble. 



" All rocks of the igneous class are presumed to have 
solidified from a molten state, either upon reaching the 
earth's surface or at varying depths below it. The 
physical conditions, such as heat and pressure, under 
which the molten rock magma consolidated, as well as 
its chemical composition and the presence of included 
vapors, are the chief features influencing the structure. 
Thus, we find the deep-seated, plutonic rocks coarsely 
crystalline with mineral constituents well defined, as 
in case of granite rocks, indicating a single, prolonged 
period of development, whereas the members of the 
extrusive, or volcanic, types, solidifying more rapidly 
at the surface, are either fine grained or frequently 
glassy and vesicular, or show porphyritic structure. 
This structure is produced by the development of large 
crystals in a more or less dense and fine-grained ground 
mass, and is caused generally by a recurrence of mineral 
growth during the effusive period of magnetic consoli- 



BROKEN-STONE ROADS. 1 29 

dation. Rocks of this kind, exhibiting a more or less 
spotted appearance, are commonly described as por- 
phyries, regardless of mineral composition, thus causing 
great confusion in the nomenclature. A movement 
in the rock magma while cooling causes frequently a 
banded arrangement of the minerals, or flow structure." 

"Igneous rocks vary in color from the light gray, 
pink, and brown of the acid granites, syenites, and 
their volcanic equivalents (rhyolite, andesite, etc.) to 
the dark steel gray or black of the basic gabbro, 
peridotite, diabase, and basalt. The darker varieties 
are commonly called trap. This term is in very general 
use and is derived from trappa, Swedish for stair, 
because rocks of this kind on cooling frequently break 
into large tabular masses, rising one above the other 
like steps, as may be seen in the exposures of diabase 
on the west shore of the Hudson River from Jersey 
city to Haverstraw. 

" The sedimentary rocks as a class represent the con- 
solidated products of former rock disintegration, as in 
case of sandstone, conglomerate, shale, etc., or they 
have been formed from an accumulation of organic 
remains chiefly of a calcareous nature, as is true of 
limestone and dolomite. These fragment al or clastic 
materials have been transported by water and deposited 
mechanically in layers on sea or lake bottoms, producing 
a very characteristic bedded or stratified structure in 
many of the resulting rocks." 

" Metamorphic rocks are such as have been produced 
by the prolonged action of physical and chemical 
forces (heat, pressure, moisture, etc.) on both sedi- 
mentary and igneous rocks alike. The foliated types 
(gneiss, schist, etc.) represent an advanced stage of 
metamorphism on a large scale (regional metamor- 



130 A, TEXT-BOOK ON ROADS AND PAVEMENTS. 

phism), and the peculiar schistose or foliated structure 
is due to the more or less parallel arrangement of 
their mineral components. The nonfoliated types 
(quartzite, marble, slate, etc.) have resulted from the 
alteration of sedimentary rocks without materially 
affecting the structure and chemical composition of 
the original material." 

The rocks commonly used for road-building may be 
classified according to their popular designations as 
trap, granite, limestone, sandstone, and chert. 

Trap. The term " trap " is commonly applied to most 
of the volcanic igneous rocks used for road-building, 
including basalt and diabase. While these rocks vary 
considerably in character, they are usually very com- 
pact and tough, and may be classed as the best material 
for roads of heavy traffic. 

* " It is characteristic of all the trappean rocks that 
they have once been fluid from heat and while in that 
state have been injected into fissures of the rocks 
through which they have found their way toward the 
present surface of the country. Only in rare cases 
have they actually passed upward to the surface of 
the earth toward which they moved; their motion was 
arrested in the lower levels of the rocks to which the 
surface has been brought down by the agents of atmos- 
pheric decay. The result of their consolidation under 
the conditions of pressure in which they cooled has 
caused these originally molten materials to be very 
compact, a state which is favored also by their chemical 
composition. This causes the materials to be very 
solid and elastic. They generally resist decay in such a 
manner that they often project above the surface, while 
the softer rocks on either side have been worn down." 

* Shaler's American Highways, p. 56. 



BROKEN-STONE ROADS. 131 

Granite. The granites, including syenite and gneiss, 
vary widely in character and differ greatly in value as 
road materials. They may be classed as next in value 
to trap for wear in the road-surface, but are somewhat 
deficient in cementing properties. 

* " In an examination of the bearing of the peno- 
logical characters upon the attrition results in this 
group three prominent factors stand out. They are: 
(1) Texture, (2) the kind of mineral, (3) the state of 
freshness of the minerals. With regard to the first of 
these it is evident that fineness and evenness of grain 
is an advantage, and that coarse grain or porphyritic 
structure is disadvantageous. It is on account of the 
granitic texture that the rocks of this group, taken as 
a whole, are not higher in the attrition scale. 

"The influence of the kind of mineral (2) is not so 
easy to determine, but, other things being equal, a 
high proportion of hornblende appears to be favorable 
to resistance; quartz in a like manner is favorable 
because of its hardness and lack of cleavage. 

" Fresh unaltered original minerals are not absolutely 
essential to a high capacity to resist abrasion; the two 
stones that take the best position in the test scale for 
this group are considerably altered — the feldspars are 
decomposed, and their substance is a mixture of smaller 
mineral units; the ferro-magnesian minerals have 
changed to chlorite and to fibrous uralitic hornblende." 

f " In the case of the igneous rocks it will be noted 
that the plutonic types with granitic granular structure 
(granite, syenite, diorite, and gabbro) are, as a rule, 
harder but inferior in toughness to their volcanic 

* Lovegrove, Attrition Tests of Road-making Stones, p. 59. 

f U. S. Department of Agriculture, Office of Public Roads, Bulletin 
3i- 



132 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

equivalents (rhyolite, basalt, and diabase). This is 
due to the more fully crystalline condition and coarser 
grain of the plutonic rocks. In the case of the volcanic 
types a compact crystal intergrowth and fine grain 
tend to increase the toughness rather than hardness of 
the material. The deleterious effect of atmospheric 
decomposition on rock texture is especially noticeable 
in the case of peridotite, andesite, and altered basalt, 
where the indifferent results of the physical tests, 
excepting cementing value, may be directly ascribed 
to the presence of such soft secondary minerals as 
kaolin, serpentine, calcite, chlorite, etc. ... As has 
already been stated in a previous paragraph, the 
cementing value is as a rule found more highly 
developed in the igneous rocks which contain alteration 
products than in their unaltered varieties. This is 
especially true in the case of diabase and basalt, rocks 
very similar in origin and mineral composition. Con- 
tinuing a step further, we note a marked decrease in 
toughness, hardness, and resistance to wear in the 
altered varieties of both these rock types over their 
fresher representatives. This is in line with what has 
already been said and indicates that the presence of 
secondary minerals in appreciable quantities, whether 
because of their softness or their indefinite semi- 
crystalline condition, weakens the original mineral 
bond and tends to destroy the primary texture of the 
rock, while at the same time furnishing the elements 
for a high binding quality in the rock powder. Valuable 
results bearing on the decomposition of rock powders 
by water have been obtained by Dr. A. S. Cushman in 
a series of interesting experiments carried on in the 
chemical laboratory of this Office. Doctor Cushman 
has shown that hydrolysis takes place in case of many 



BROKEN-STONE ROADS. 133 

rock powders the moment they are wet, thus pro- 
ducing secondary products (hydrated silicates) of a 
colloidal nature which greatly increase the binding 
power. This points finally to the conclusion that the 
mineral analysis of igneous rocks, besides providing a 
convenient means for comparison and classification, 
serves to a certain extent as a measure of their physi- 
cal properties." 

Limestone. Limestones commonly possess the 
cementing power in fair degree, although lacking in 
hardness and resistance to abrasion. The cementing 
power has probably been commonly overestimated, 
because of the softness of the rock and the ease with 
which it usually packs in the road surface. Limestones 
are the most widely distributed and most generally 
used materials for road surfaces. They differ very 
widely in character, some forming an excellent material 
under moderate traffic and others being so soft as to 
offer little resistance to wear. 

* "In proportion as limestone becomes crystalline, 
i.e., takes on the character of marble, its value in road- 
making diminishes, for the reason that the c^stalline 
structure in most cases so far weakens the mass that 
it is apt readily to pass into the state of powder. As 
these marbles occur only in districts where better road- 
making materials are likely to be present, they may not 
be further mentioned, except to say that their use is 
commendable for foundation layers, where their fair 
cementation value makes them tolerably fit for service. 
So long as the bits are kept from the destructive action 
of the wheels and feet of the carriages and horses, they 
lend themselves to the road-master's use. Even where 
a more resisting top covering of ordinary broken stone 
* Shaler's American Highways, p. 61. 



134 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

cannot be provided, a tolerable road can be made of 
this material, often very cheaply by using the waste 
from quarries, by covering the surface with a coating 
of ferruginous matter, such as is afforded by the leaner 
iron ores, or by using a top coating of gravel." 

# " If we take the pure dolomites alone, it is clear that 
those behave best in the attrition test which have 
a fine-grained, even, granular texture with irregular- 
shaped grains interlocking closely one with another, 
and with a general absence of porous cavities. A dolo- 
mite is by no means always better than a limestone, 
but the best type of dolomite will be more resistant 
than the best limestones, being harder. 

" Among the limestones, those stand highest that are 
composed of a mixed assemblage of small organic 
remains, notably of foraminifera, and possess at the 
same time a somewhat bituminous composition (this 
characteristic is often associated with foraminifera in 
carboniferous limestone). Crinoidal limestones do not 
stand so high, evidently on account of the ready 
cleavage of the particles of calcite, which is not only 
a soft mineral but has an extremely perfect cleavage, 
hence it wears rapidly and crumbles easily under 
repeated small blows; but if the crinoid fragments 
are small and uniform in size, set in a matrix of fine 
calcareous matter, the stone may compare well with 
other limestones. " 

Sandstone. As a class sandstones are deficient in 
cementing power and do not stand well in the surface 
of . a road. They have commonly been sweepingly 
condemned and rejected by road-builders. In some 
instances, however, sandstones have given good 
results, and some of them possess fairly good cementing 
* Lovegrove, Attrition Tests of Road-making Stones, p. 61. 



BROKEN-STONE ROADS. 135 

power. The value of a sandstone depends mainly 
upon the character of the cementing medium; where 
this is of siliceous character, a high degree of hardness 
and resistance to wear may result. 

* "Considering the next important group of road- 
making rocks, we notice here also a marked coincidence 
in mineral composition and physical properties. The 
soft and nonresistant calcareous rocks (limestones, 
dolomites, and calcareous sandstones), composed largely 
of calcite and dolomite, are, as would be expected, 
inferior in hardness, toughness, and wearing qualities 
to the more siliceous sandstones and cherts/' 

Chert. Chert is a very hard material and shows 
good resistance to wear. It is somewhat low in cement- 
ing value, but when carefully used forms a good road 
material. It is quite variable in character and needs 
careful selection. Chert is commonly found in a 
finely divided condition, and can be used, in many 
instances, without crushing. It occurs throughout 
many of the Southern states, where it is found widely 
distributed and is the only available material for such 
work. 

* " The low cementing value of chert obtained by 
laboratory tests is not in every case in accordance with 
that developed by this rock under traffic. In dis- 
cussing the origin of road material it has been stated 
that chert or flint belongs to that class of sedimentary 
rocks whose mineral components have been formed 
largely by chemical precipitation and were originally 
of a colloidal or amorphous nature. The highly 
fractured condition of many cherts is probably due in 
large measure to shrinkage caused by a decrease in 

* U. S. Department of Agriculture, Office of Public Roads, Bulletin 
3i- 



136 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

volume in passing from an amorphous to a crystalline 
state. Although no experiments have as yet been made 
on the solubility of this material, it seems to the writer 
very probable that the dissolving action of road waters 
on finely divided chert dust is relatively high and that 
the high binding power of some of these rocks is 
caused by hydrated opaline silica resulting from a 
decomposition of this kind. The fact that in certain 
Localities surface flints are superior to quarry flints 
for road making is suggestive in this connection." 

Mr. Lord, in the bulletin already quoted, gives tables 
showing the average mineral composition and plates 
showing structure of the various rocks, and indicates 
that the probable value of a rock for road-building 
may be inferred from its mineral composition and 
structure. 

" To explain the bearing of mineral composition and 
structure on the physical properties of rocks, it has 
been found necessary to define these properties and 
describe the various methods for testing road materials. 
The results of these tests have been used in correlating 
the physical properties of the various rock families 
with their mineral components, and the following 
conclusions have been reached: 

"(1) Igneous and metamorphic rocks, owing to a 
high degree of crystallization and a preponderance of 
silicate minerals, offer a greater resistance to abrasion 
than nearly all varieties of sedimentary rocks. 

" (2) The coarse-grained intrusive rocks of the igneous 
class are harder, but. break more readily under impact 
than the finer-grained volcanic varieties of like mineral 
composition. 

" (3) The deleterious effect of atmospheric weathering 
on the wearing qualities of rocks has been demonstrated. 



BROKEN-STONE ROADS. 137 

"(4) The cementing value of rocks is, to a certain 
degree, measured by the abundance of secondary 
minerals resulting from rock decay. 

" (5) Metamorphic rocks have, as a rule, a low bind- 
ing power, owing to a regeneration of secondary 
minerals and to the effects of heat and pressure. The 
foliated types part readily along planes of schistosity 
and therefore are not well adapted to road con- 
struction. 

"(6) The quantitative mineral analysis of rocks 
serves to a certain extent as a measure of their useful 
properties for road construction. " 

•Art. 37. Methods of Testing Stone. 

Final judgment concerning the value of stone for 
road purposes, or the best method of using it, can only 
be formed through experience with the material in use. 
Tests may, however, be applied which will throw much 
light upon the probable value of a material, or which 
may give an idea of the probable relative values of 
different available materials in a particular case. 
These tests are of two kinds: I. Determination of 
the mineral composition through petrographic analysis. 
2. Tests of the physical properties of road materials. 

PETROGRAPHIC ANALYSIS. 

The following methods of examination have been 
used by the Office of Public Roads of the U. S. Agri- 
cultural Department, and are described by Mr. Edwin 
C. E. Lord in Bulletin No. 31, August, 1907. 

"Upon receipt of the rock sample, which, accord- 
ing to the specification of this Office, should weigh not 



138 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

less than 30 pounds and be collected with care to repre- 
sent as nearly as possible an average of the whole 
exposure, it is examined in a general way to determine 
the proper method of analysis. 

"Rocks consisting essentially of the carbonates of 
lime and magnesia (limestones, dolomites, etc.), as 
well as fine-grained shales and unconsolidated sedi- 
mentary deposits, such as clays, sands, gravels, etc., 
are analyzed chemically when necessary, whereas all 
other materials are prepared for microscopic exami- 
nation or determined macroscopically. 

"The mineral composition of a rock may, under 
favorable conditions, be estimated with considerable 
accuracy by a macroscopic examination, yet for exact 
quantitative results the aid of a polarizing microscope 
and transparent thin sections of the rock are essential. 

Macroscopic Method. " The macroscopic form of 
analysis can be applied only to coarse-grained rock, in 
which the various mineral components are easily 
detected with the unaided eye. The approximate 
volumetric relations of these minerals may be deter- 
mined by preparing a smooth surface of the rock 
sample and covering it with a transparent celluloid 
scale divided into 100 equal square areas and estimat- 
ing the minerals present from the number of areas 
covered by each mineral. Any properly graduated 
scale can be used, but a transparent one is preferable. " 

Microscopic Methods. "Owing to the large amount 
of material received in this laboratory it has been 
found necessary to perfect a more rapid method of 
quantitative analysis than any hitherto described. 

"The laboratory is equipped with an exceptionally 
good petrographic microscope of the latest Fuess model, 
which, beside the usual attachments, is provided with 



BROKEN-STONE ROADS. 1 39 

a revolving analyzer in the tube to aid in the deter- 
mination of very low double refracting minerals, and 
a Schwarzmann scale for the measurement of optical 
axial angles. 

"Another important accessory is a detachable 
screw-micrometer, movable in the focal plane of the 
ocular by means of a drum screw, which, with the 
most powerful objective (one-twelfth-inch oil immer- 
sion), records a drum-interval of 0.00004 mm. The 
measuring apparatus devised by Mr. L. W. Page and 
used for the mineral determinations consists of an 
ordinary fixed eyepiece having a square field divided 
into 100 quadratic areas. With the aid of this cross- 
line field, each square of which is one one-hundredth 
of the whole field, the relative proportions, expressed 
in per cent, of the minerals occupying the field can be 
readily determined by simply noting the number of 
squares covered by each mineral in turn. Averages 
derived from numerous examinations of this kind in 
various parts of the section indicate the percentage of 
the different minerals constituting the rock itself. " 

"Experience has shown that with a large majority 
of rock samples twenty determinations, using a magni- 
fication of 52 diameters, give very satisfactory results. 
In the case of extremely fine-grained rocks, however, 
it is best to use a three-quarter-inch objective lens 
which enlarges 105 diameters when combined with the 
eyepiece micrometer. 

"With rocks having an average grain exceeding 
5 mm., or those varying greatly in texture, as in the 
case of porphyritic and schistose varieties, it is in 
some instances well to employ a two-inch objective in 
combination with an ocular prepared in the same 
manner as that just described, but divided into only 



140 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

25 square areas and magnifying 30 diameters. In 
the case of these exceptionally coarse-grained rocks, 
two or more thin sections of the same sample are 
examined before reliable results can be obtained." 



PHYSICAL TESTS. 

The physical properties of stone for road-building 
are commonly tested by determining the percentage 
of wear, using the Deval abrasion apparatus, and the 
cementation properties by the use of the Page cementa- 
tion test. Tests are also sometimes made of the crush- 
ing strength, resistance to impact, and resistance to 
abrasion by grinding, and, in some instances, the 
specific gravity and absorption of the rock are deter- 
mined. 

Abrasion Test. This test was first used in France, 
and is commonly known as the Deval test, bearing the 
name of its designer. The Deval machine consists of 
cylinders 20 cm. in diameter and 34 cm. in depth, 
closed at one end and with a tightly fitting cover for 
the other. Two or four of these cylinders are mounted 
upon a horizontal shaft so that the axis of each cylinder 
is inclined at an angle of 30 degrees with the axis of 
rotation. 

The method of conducting the test in the investiga- 
tions of the U. S. Office of Public Roads is as follows: * 
"The sample to be tested is first broken in pieces that 
will pass in all positions through a 6 centimeter (2.4 
inch) ring. The stones are then cleansed, dried in a 
hot-air bath at 100 degrees C, and cooled in a desiccator. 
Five kilograms are weighed and placed in one of the 
cylinders, the cover bolted on, and the machine rotated 

♦Bureau of Chemistry, Bulletin No. 79. 



BROKEN-STONE ROADS. 141 

at the rate of 2000 revolutions per hour for 5 hours. 
When the 10,000 revolutions of the machine are com- 
pleted the contents of the cylinder are placed on a 
sieve of 0.16 centimeter ( T V inch) mesh, and the 
material which passes through is again sifted through 
a sieve of 0.025 centimeter (0.01 inch) mesh. Both 
sieves and the fragments of rock remaining on them 
are held under running water till all adhering dust is 
washed off. After the fragments have been dried at 
100 degrees C. and cooled in a desiccator they are 
weighed, and their weight subtracted from the original 
5 kilograms (11 pounds). The difference obtained 
is the weight of the detritus under 0.16 centimeter 
(^ inch) worn off in the test. " 

In the French experiments it was found that the 
best grades of rock gave about 20 grams of detritus 
per kilogram of rock tested, and the number 20 was 
adopted as a standard and the "coefficient of wear" 
determined from the formula: 

^ rr • r 20 400 

Loemcient 01 wear = 20 X 777- = -777- * 

W W 

in which W is the weight in grams of detritus under 
0.16 centimeter (^ inch) in size obtained per kilo- 
gram (2.2 pounds) of stone. The French coefficient 
is sometimes used in stating results in American tests, 
but it is more common to ues the "percentage of 
wear/' which is found by stating the weight of detritus 
under 0.16 centimeter in terms of percentage of the 
weight of rock tested. In this case, 

■r. r 4° 

Percentage 01 wear = - — — • 

Loemcient 01 wear 

In some of the work of the United States Agricul- 
tural Department another coefficient, known as the 



142 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

United States Agricultural Department coefficient of 
wear, has been employed. This coefficient is found by 
subtracting 4000 grams from the weight of the frag- 
ments over 3 centimeters (1.2 inches) which remain 
after the test and dividing the difference by 10. By 
this method, if 20 per cent of the material is abraded 
from the original 5000 grams, the coefficient is and 
the material considered worthless; if no dust is worn 
off, the coefficient is 1 00. 

The Committee on Standard Tests for Road Materials, 
of the American Society for Testing Materials, in 1904 
recommended the following specification for the 
abrasion test: "The machine shall consist of one or 
more hollow iron cylinders, closed at one end and 
furnished with a tightly fitting iron cover for the 
other; the cylinders to be 20 centimeters in diameter 
and 34 centimeters in depth inside. These cylinders 
are to be mounted on a shaft at an angle of 30 degrees 
with the axis of rotation of the shaft. 

" At least 30 pounds of coarsely broken stone should 
be available for a test. The rock to be tested should 
be broken in pieces as nearly uniform as possible, and 
as nearly 50 pieces as possible shall constitute a test 
sample. The total weight of rock in a test should be 
within 10 grams of 5 kilograms. All test pieces should 
be washed and thoroughly dried before weighing; 
10,000 revolutions at the rate of between 30 and S3 to 
the minute, must constitute a test. Only the per- 
centage of material worn off which will pass through 
a 0.16 centimeter mesh sieve should be considered 
in determining the amount of wear. This may be 
expressed either in the per cent of the 5 kilograms 
used in the test, or the French coefficient, which is in 
more general use, may be given." 



BROKEN-STONE ROADS. 1 43 

Cementation Test. This test was developed by 
Mr. Logan Waller Page while geologist of the Mas- 
sachusetts Highway Commission. It consists in grind- 
ing the stone into dust, wetting and moulding the 
dust into a small cylinder, which is dried and then 
tested by subjecting it to the impact of the falling 
weight. The method of conducting this test as used 
by the Office of Public Roads of the United States 
Department of Agriculture is as follows: "One 
kilogram of the rock to be tested is broken sufficiently 
small to pass a 6 millimeter but not a I millimeter 
screen. It is then placed in a ball mill and is ground 
for two hours and a half. This ball mill contains two 
chilled iron balls which weigh 25 pounds each, and is 
revolved at the rate of 2000 revolutions per hour. It 
was found by experiment that grinding rock thus pre- 
pared for two hours and a half was sufficient to reduce 
it to a powder that would pass through a 0.25 milli- 
meter mesh. The dust thus obtained is mixed with 
water to about the consistency of a stiff dough, and 
is kept in a closed jar for twenty-four hours. About 
25 grams of this dough is placed in a cylindrical metal 
die 25 millimeters in diameter. A closely fitting plug, 
supported by guide rods, is inserted over the material, 
which is then subjected to a pressure of 100 kilograms 
per square centimeter. 

" It is most important that these briquettes should 
be compressed in a uniform manner, and for this a 
special machine has been designed. The die is placed 
on an iron platform supported by a piston rod, which 
is connected directly with a hydraulic piston below. 
Water from a tank is admitted to the hydraulic cylinder 
through a small orifice in the pipe. As the piston 
rises the platform and die are carried up with it, the 



144 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

plug of the latter coming in contact with a yoke 
attached to a properly weighted lever arm. When the 
lever arm is raised one-eighth of an inch it closes an 
electric circuit which trips a right angle cock, shutting 
off the water and opening the exhaust. One minute is 
required to compress a briquette, and the maximum 
load is applied only for an instant. By this device 
practically uniform conditions are obtained. 

"The height of the briquette is measured, and if it 
is not exactly 25 millimeters the required amount of 
material is added or subtracted to make the next 
briquette the required height. Five briquettes are 
made from each test sample, and allowed to dry 
twelve hours in air and twelve hours in a steam bath. 
After cooling in a desiccator they are tested by impact 
in a machine especially designed for the purpose/' 

The machine commonly used for this purpose is 
known as the Page- Johnson Impact Machine. It was 
designed by Mr. L. W. Page and afterward modified 
by Mr. A. N. Johnson. The blow is delivered by a 
hammer weighing one kilogram striking upon a 
flat -end plunger, which is pressed upon the briquette 
by two light spiral springs. The standard fall of the 
hammer for a test is I centimeter (0.39 inch), and 
this blow is repeated until the bond of cementation of 
the material is destroyed. The number of blows 
required is noted and the average obtained upon five 
briquettes is given as the cementing value. 

In making this test the results may be considerably 
affected by slight differences in manipulating the 
material. It is important that the same amount of 
kneading be used in all tests and that the dough should 
be allowed to stand at least 24 hours before forming 
the cylinders. 



BROKEN-STONE ROADS. 1 45 

Grinding Test. The test for abrasion by grinding 
is sometimes used in France, where it is known as the 
Dorry test. It has also been used by the Office of 
Public Roads at Washington. The object of the test 
is to give a measure of the hardness of the rock. It 
gives interesting information concerning the material, 
but is not of special value in testing road material. 
The test is made as follows: "The test piece in the 
form of a cylinder about 3 inches in length by I inch 
in diameter is prepared by an annular core drill and 
placed in the grinding machine in such a manner that 
the base of the cylinder rests on the upper surface of 
a circular grinding disk of cast iron, which is rotated 
in a horizontal plane by a crank movement. The 
specimen is weighted so as to exert a pressure of 
250 grams per square centimeter against the disk, 
which is fed from a funnel with sand of about i£ 
millimeters in diameter. After 1 000 revolutions the 
loss in weight of the sample is determined and the 
coefficient of wear obtained by deducting one-third 
of this loss from 20." 

Impact Test. This test is intended as a measure of 
the toughness of the material. It is frequently made, 
although not of special value as a test for road material. 
It is made as follows: 'The test piece is a cylindrical 
rock core similar to that used in determining hardness 
and the test is made with an impact machine con- 
structed on the principle of the pile driver. The blow 
is delivered by a hammer weighing 2 kilograms, which 
is raised by a sprocket chain and released automatically 
by a concentric electro-magnet. The test consists of a 
I centimeter fall of the hammer for the first blow and 
an increased fall of 1 centimeter for each succeeding 
blow until the failure of the test piece occurs. The 



146 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

number of blows required to cause this failure repre- 
sents the toughness. " 

The abrasion and cementation tests are frequently 
employed for the purpose of comparing the properties 
of various road stones, and afford a means by which a 
judgment may be formed as to the probable relative 
values of various materials for road construction. No 
fixed standard for comparison has been devised, and the 
relative importance of the various properties depends 
upon the character of the road to be constructed. 

Art. 38. Road Metal. 

Stone is prepared for use in road work by crushing and 
screening. In the early days of broken-stone roads, 
all stone was broken by hand, and the roads were care- 
fully constructed of stone broken to approximately uni- 
form sizes without the addition of a binding material. 
The development of stone crushing machinery has, 
however, modified practice in this regard and stone 
crushed by machinery is now almost exclusively used. 
It gives satisfaction both as to binding properties and 
durability, and has the advantage of greatly lessening 
the cost. 

The size to which stone should be broken for road 
material depends to some extent upon the nature of 
the material. The harder and tougher it is the smaller 
the pieces may be without danger of crushing or shat- 
tering under the loads and shocks received in the road 
surface, and the smaller also they will need to be in 
order to be thoroughly compacted in the road. 

It is a general custom to use larger stones in the 
bottom courses of a road than at the top. A rule very 
commonly given is that the stones for the lower layers 



BROKEN-STONE ROADS. I 47 

should be at least 2 inches in their greatest diameter, 
and not more than 3 inches, and that for the surface 
layer the stones shall not be greater than 2 inches 
in greatest dimension. 

If of very hard rock the surface layer may have I 
inch to i£ inches as an upper limit of size. 

The size of the rock in the lower layers does not 
seem of so great importance as that for the surface 
layers, as it is not directly subject to the weight or the 
abrading action of the concentrated wheel-loads, and it 
is probable that in some cases unnecessary expense is 
incurred in following the refinements of rigid specifica- 
tions in this particular. 

There is a difference of opinion also among road- 
builders as to the advisability of using stone of uniform 
size. Some insist quite strenuously upon this point 
and carefully screen their stone with the object of get- 
ting it as uniform as possible; while others declare that 
the variation of size is an advantage, and even that the 
stone should not be screened after coming from the 
crusher, except to remove the stone above the limiting 
size and when necessary to get rid of foreign matter 
in case it should contain claj^ or earth. 

Uniformity of size probably makes the wear more 
even, but the presence of smaller fragments facilitates 
the binding together of the material. The best prac- 
tice seems to favor the exclusion of the fine material 
from the stone, without insisting on too great uniform- 
ity in size (stones being allowed probably from \ inch 
to I J or 2 inches in dimension), and then adding small 
material after the placing of the stone upon the road 
to assist binding. If the varying sizes be well dis- 
tributed through the mass of stone, the variation of 
size has the advantage of lessening the amount of voids, 



148 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and makes possible to compact the stone in the road 
with a less quantity of binder. Screening out the fine 
parts and dust eliminates the danger of having portions 
of the road made up entirely of fine material, and 
secures a proper distribution of the binder through 
the mass of stone. 

Gravel is frequently used for roads constructed in 
the same manner as with broken stone, both with and 
without the telford foundation. The requirements of 
a good gravel for this purpose are the same as for a 
good stone. The stones of the gravel should be sharp 
and angular, and must possess the qualities of hardness 
and toughness. Water-worn material is therefore ob- 
jectionable, as it will not compact without the use of 
large amounts of soft binding material. In many 
places a hard flint gravel occurs which is not inferior to 
the best broken stone. This frequently occurs when 
the available rock is soft ' limestone and may be used 
to advantage as a surface upon a base of the soft rock. 

Gravel should be screened to remove the larger stones 
and the fine material, and then treated in the same 
manner as broken stone. 

Gravel not fit for surface material may often be used 
to advantage as a base under a surface of hard rock; 
in many instances, economy would result from the 
substitution of gravel for broken stone in such work. 
Slag and cinders may also sometimes be used in the 
same manner. 

In the work of the Massachusetts Highway Commis- 
sion: "All broken stone used is separated into three 
sizes by passing it through a screen with meshes £ inch, 
1^ inches, and 2\ inches in diameter. The largest size 
is placed at the bottom and is covered with the succes- 
sive smaller sizes, The different sizes of stone are 



BROKEN-STONE ROADS. 1 49 

spread in courses. The sub-grade and each course of 
stone are rolled thoroughly, and the top course is 
watered before rolling. " 

It was the practice of McAdam to require that all 
the stone used upon his roads should be as nearly as 
possible of a uniform size, and that no foreign sub- 
stance be mixed with it. In more recent practice it 
has been found advantageous to use a certain amount 
of finer material to fill the interstices between the 
stones, and thus aid in the compacting of the road as 
well as render it less pervious. Some engineers place 
a thin layer of binding material upon the surface of 
the road and work it into the surface voids, while 
others distribute the binding material through the 
entire mass of stone composing the road. 

It is agreed that an impervious surface cannot be 
formed of blocks of hard broken stone without the ad- 
dition of some small material to fill the voids. It has 
also been found that when the rock is hard, such as is 
needed for good wear in a road surface, it will compact 
with difficulty, and that a certain amount of binding 
material is necessary in order that the road may be 
brought to a surface. 

Binding material may consist of the screenings from 
the broken stone used in the road, of sand or small 
gravel, or of loam. Loam has been used in some 
instances with satisfactory results, but the wisdom of 
its use is questioned by most road builders. When 
sand is used, it should contain a considerable admix- 
ture of fine particles, and will usually be improved by 
the addition of some fine screenings. The presence 
of considerable dust in a finely divided condition is 
important in securing the binding together of the 
road surface. 



150 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In cases where local stone is being used for the lower 
courses of a road to be surfaced with trap or other 
more durable rock, or where a flint gravel surface is 
used upon a soft limestone base, the screenings from 
the stone used in the lower layer may often advan- 
tageously be used in binding the surface, the whole 
run of the crusher except the screenings through about 
a one-half inch screen being used in the lower course of 
the road. 

In some instances the binding material is mixed with 
the surface stone before placing upon the road. The 
following extract from the specifications of Mr. James 
Owen for roads in Essex County, New Jersey, shows 
this practice: "When the two courses are rolled to 
the satisfaction of the Engineer and Supervisor, a coat 
of fifty (50) per cent of three-quarters (f) inch stone 
and fifty (50) per cent of screenings properly mixed 
is to be spread of sufficient thickness to make a smooth 
and uniform surface to the road; then again rolled 
until the road becomes thoroughly consolidated, hard 
and smooth. " This specification is remarkable for 
the large quantity of screenings used, and needs great 
care in securing a proper mixture of the two materials. 

Art. 39. Compacting the Road. 

The materials may be compacted in a road either by 
placing them in position and allowing the traffic to 
pass over them or by rolling with a steam or horse 
roller. 

The first method by itself is seldom practiced when 
it is possible to avoid it. It is hard upon the traffic, 
takes a long time to reduce the road to compact con- 
dition, and a smooth surface is with difficulty pro- 



BROKEN-STONE ROADS. 151 

duced. Where heavy horse rollers are employed they 
are clumsy and inconvenient to handle, and the work 
of rolling is slow as compared with the steam roller. 
In many instances, however, good results are obtained 
with them. They are not so expensive in first cost as 
steam rollers, and have not the disadvantage of fright- 
ening horses. 

Horse rollers are usually arranged so that the direc- 
tion of motion may be reversed without turning the 
roller itself around, and also so that the weight may be 
changed by placing additional weight inside the roller 
or removing it. Horse rollers for this purpose usually 
bring a pressure of from 125 to 250 pounds per linear 
inch upon the road and weigh from 3 to 6 tons. 

Steam rollers weighing from 8 to 15 tons are most 
commonly employed for compacting the road mate- 
rials. They have the advantage of forcing the materials 
at once into a firm and compact mass and producing a 
smooth surface for the immediate use of travel. They 
admit also of the use of hard materials for binding. 
These rollers give a pressure under the drivers of from 
400 to 650 pounds per linear inch. 

The stone forming the body of the road should be 
placed and partially compacted before the addition of 
the small material, which may then be worked into the 
spaces between them. 

The office of the binding material is to hold the 
stones in place and form a bearing for them, as well as 
to prevent the passage of water between them. It has 
no duty to perform in sustaining the loads. This is 
the objection to having the binding material mixed 
with the stones in advance, as would be the case when 
unscreened stone is used. A portion of the road stones 
would be replaced by small material instead of having 



152 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

this material only in such voids as necessarily exist be- 
tween the stones. 

The quantity of binding to be used is that which 
will be barely sufficient to fill all the voids in the larger 
material. It has been contended that the lower por- 
tion of the road should be porous in order to facilitate 
the escape of any water that may find its way through 
the surface, but the tendency of the best modern prac- 
tice is in the direction of filling all the voids as nearly 
as possible, thus making the entire road practically one 
solid body, and it is now commonly agreed that the sur- 
face of a properly constructed broken-stone road is very 
nearly impervious to water. 

The voids in loose broken stone comprise about 40 
to 50 per cent of the volume. In the stone when 
compacted in the road the voids are somewhat reduced, 
probably ranging from 30 to 40 per cent of the volume. 
The voids may be approximately determined in any 
case by filling a measure with the stone, shaken down 
as closely as possible, and then measuring the quantity 
of sand that can be added in the same manner. 

In constructing a road with the use of a steam-roller, 
the road-stone is first put on to the required thickness 
and the roller passed over it to settle the stones into 
place and reduce the voids as much as possible. The 
binding material, representing a volume about equal to 
the voids in the stone, is then added, sprinkled, and 
rolled until the small material is washed and forced into 
the interstices, giving a smooth, hard surface. This is 
repeated for each layer of stone, or in some cases the 
small material is applied only to the top layer. 

A thin coating of the binding material is then spread 
upon the surface and the road thrown open for travel. 



broken-stone roads. 1 53 

Art. 40. Thickness of Road-covering. 

The thickness necessary for a road-covering depends 
upon the amount of the traffic it is to bear and upon the 
nature of the foundation afforded by the road-bed. 
Under a heavy traffic it is advisable to make the road- 
covering heavier than might be allowable for lighter 
traffic, in order to provide for wear and lessen cost of 
renewals. 

When the road-bed is firm, well drained, and not 
likely to soften at a wet season, it will always afford a 
firm bearing, upon which the covering may rest. The 
loads coming upon the road are then simply transmitted 
through the covering to the road-bed beneath, and 
there is no tendency on the part of the loads to break 
through the covering other than by direct crushing of 
its material. If, however, the road-bed may become 
soft in wet weather, it will then lose its power to firmly 
sustain the covering at all points, and the covering 
must possess sufficient strength to bridge over places 
where it is not supported from beneath, or a load com- 
ing upon it may break through by bending it down- 
ward at such point. The thickness of road-covering, 
therefore, must be greater where the road-bed is less 
perfect. 

The intensity of freezing that may be expected also 
has an influence upon the necessary thickness of the 
road-covering. The effect of frost upon the road will 
depend in large measure upon the condition of the 
road-bed, and thus make the thickness depend in still 
greater measure upon its nature. Freezing will not 
injure a dry road-bed, but if. it be damp and have but 
a thin covering the road is likely to blow or be thrown 
up by the action of frost. 



154 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

For roads on considerable grades the thickness of the 
road-covering is often reduced below what is used on 
flat ones, because of the better drainage afforded by 
the slopes. It is to be remarked, however, that if the 
slopes are very steep the wear of the surface becomes 
so great, due to the horses' efforts to obtain foothold 
and to the washing of surface-waters during rains, 
that the thickness of the coating should be increased. 

Macadam roads are commonly made from 4 to 12 
inches thick, and telford roads from 8 to 12 inches, of 
which 5 to 8 inches may be foundation pavement. 

A covering 6 to 8 inches thick is usually sufficient for 
nearly any case of a country road, unless laid upon bad 
foundation, or to carry exceptionally heavy traffic. 
When the road-bed is formed of firm material and well 
drained, a covering of 4 or 5 inches of broken stone or 
gravel may give good service under considerable traffic. 

A thin road to be effective must have its interstices 
well filled with binding material and be thoroughly 
compacted by rolling. It will then present no voids to 
be filled by the soil pressing upward from below, and 
at the same time it will be practically impervious and 
prevent surface-water from reaching the road-bed, thus 
keeping the material in good condition to sustain the 
loads. The 4-inch roads of Bridgeport, Conn., which 
are often cited as examples of successful work, are con- 
structed in this manner of exceptionally good mate- 
rial. In other cases where thin roads have proved fail- 
ures the trouble may often be traced to dampness in 
the subsoil or to lack of thorough construction. 

Instances will frequently be met in practice where a 
road must be constructed over material which is likely 
to be unstable and cannot be made firm by drainage. 
In such cases, thick roads must be built. Where the 



BROKEN-STONE ROADS. 155 

conditions are unfavorable, a road 12 to 16 inches thick 
may be necessary. 

In many cases the problem to decide, in determining 
the thickness of a covering, is whether to use heavy 
construction or thorough drainage. It is easier to get 
good results with thick road-coverings, and they are 
in general safer to use; but skillful adaptation of less 
material may often save expense in construction with 
good results. The peculiar conditions of each case must 
decide what is best for that case. 

On country roads the macadam surface should be 
given a crown of from one-thirtieth to one-twenty- 
fourth of the width in order to provide good drainage. 
In manyinstances a considerable saving in road material 
may be effected by making the road thinner at the 
edges than in the middle. The Massachusetts Highway 
Commission in some instances reduce the thickness of 
their 6-inch roads to 2\ or 3^ inches at the edges. 
Some engineers grade the road-bed without leaving a 
bench at the side, and reduce the stone to thin edges. 
It is doubtful if there is any economy in this practice, 
as it is wasteful in the use of stone, although it effects 
a small saving in the cost of grading the road-bed. 

Art. 41. Maintenance of Broken-stone Roads. 

To maintain a broken-stone road in good condition 
it is necessary first of all that it be frequently cleaned 
of mud and dust, and that the gutters and surface 
drains be kept open to insure the prompt discharge 
of all water that may come upon the surface of the 
road. 

The best method of making repairs that may become 
necessary to the road-surface depends upon the char- 



I56 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

acter of the material composing the surface and the 
weight of the traffic passing over it. 

If the road metal be of soft material which wears 
easily, it will require constant supervision and small 
repairs whenever a rut or depression may appear. 
Material of this kind binds readily with new material 
that may be added, and may in this manner frequently 
be kept in good condition without great difficulty, while 
if not attended to at once when wear begins to show it 
will very rapidly increase, to the great detriment of the 
road. In making repairs by this method, the material 
is commonly placed a little at a time and compacted by 
the traffic. The material used for this purpose should 
be the same as that of the road-surface, and not fine 
material which would soon reduce to powder under the 
loads which come upon it. By careful attention to 
minute repairs in this manner a surface may be kept 
in good condition until it wears so thin as to require 
renewal. 

In case the road be of harder material that will not 
so readily combine when a thin coating is added, the 
repairs may not be so frequent, as the surface will not 
wear so rapidly and immediate attention is not so 
important. It is usually more satisfactory in this case 
to make more extensive repairs at one time, as a larger 
quantity of material added at once may be more readily 
compacted to a uniform surface, the repairs taking the 
form of an additional layer upon the road. 

Where the material of the road-surface is very hard 
and durable, a well-constructed road may wear quite 
evenly and require very little, if anything, in the way 
of ordinary small repairs until worn out. It is now 
usually considered the best practice to leave such a 
road to itself until it wears very thin, and then renew it 



BROKEN-STONE ROADS. 1 57 

by an entirely new layer of broken stone placed in the 
same manner as in original construction, on top of the 
worn surface, and without in any way disturbing that 
surface. If a thin layer only of material is to be 
added at one time, in order that it may unite firmly 
with the upper layer of the road it is usually necessary 
to break the bond of the surface material before plac- 
ing the new layer, either by picking it up by hand or, 
if a steam roller is in use, by means of short spikes, in 
its surface. Care should be taken in doing this, how- 
ever, that only the surface layer be loosened, and that 
the solidity of the body of the road be not disturbed, 
as might be the case if the spikes are too long. 

The maintenance of macadam roads under trying 
conditions or under severe traffic has in many instances 
proven a matter of considerable difficulty and of large 
expense. The great development of automobile travel 
has introduced a new element into the problem and 
greatly increased the difficulties of road maintenance. 
These vehicles, moving rapidly upon rubber tires, exert 
a lifting action upon the surface of the road, draw- 
ing the binder out in the form of dust, and leaving 
the surface loose. Under ordinary circumstances the 
destruction of a broken-stone road is greatest in dry 
and dusty weather. If the road is subject to consider- 
able travel, wear becomes rapid and a certain amount 
of the road metal is blown away by the wind, washed 
away in case of rain, or cleaned from the surface as 
mud. The binding material wearing into dust and 
being removed from the road loosens the stones of the 
road-surface, causing the road to " ravel. " 

Much difficulty has also been experienced m some 
localities, where the macadam roads connect with 
earth roads which in wet weather are composed of 



158 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

heavy, sticky mud, on account of the " picking up " of 
the macadam surface in muddy weather by the wheels 
of vehicles which are covered with mud. The stones 
in the surface are loosened and carried off until the road 
is destroyed. 

To protect a broken-stone road against excessive 
wear and prevent raveling in dry weather, some 
means of laying the dust must be used. Sprinkling 
the road-surface with water is often used for this 
purpose, and has an important effect in reducing the 
wear and prolonging the life of the road. If the road 
be systematically sprinkled, the material ground off 
by the traffic will pack upon the surface, forming a 
cushion which serves to protect it from further attri- 
tion. In sprinkling, the object should be to keep the 
surface damp, and not to flood it by applying too 
large a quantity of water at once. 

Oil and tar are also used for laying dust in the 
maintenance of macadam roads. The use of oil in 
road construction in California has already been dis- 
cussed in Art. 29, and the surfaces of macadam roads 
have also been sprinkled with oil in a number of eastern 
towns for the purpose of laying dust. This usually 
requires from one to three applications of oil during the 
season and has been found much cheaper than sprin- 
kling with water. It is probable also that some treat- 
ment of this nature will be found of value in preventing 
the "picking up" of a road surface by mud. Tar is 
also frequently used in much the same manner as oil 
in laying dust and preventing the raveling of the surface. 
The construction of tar roads will be separately con- 
sidered in Art. 42. 



BROKEN-STONE ROADS. 159 

Art. 42. Bituminous Macadam. 

The term "tar macadam" or sometimes "bitumi- 
nous macadam" has been used to cover the use of 
bituminous materials for bonding together or preserv- 
ing the surface of broken-stone roads in a variety of 
ways. In some instances, the tar is only used to coat 
the surface of a macadam road, with a view to prevent 
the formation of dust and the raveling of the road; 
in others, the tar is mixed with the broken stone used 
in building the road to form a bituminous concrete 
before laying it on the road. 

Tar Macadam in England. Tar macadam pave- 
ments have been used for quite a number of years in 
England, and have met with fairly good success. The 
usual method of construction, in England, is to first 
dry the stone by heating it upon a hot hearth. The 
tar is boiled for three or four hours and is then mixed 
with the hot stone, and turned with hot shovels. The 
stone is graded usually into two or three sizes; the 
larger stone, from 1 to 2 inches in diameter, is used for 
the bottom layer; the stone from one-half to I inch, for 
the upper layer; and sometimes the fine stone, from one- 
quarter to one-half inch, is used on top to fill the inter- 
stices in the surface layer. The quantity of tar varies 
from 8 to 12 gallons per cubic yard of stone. Each 
layer is separately rolled, and the top is covered by a 
coating of stone screenings. In some instances, the 
lower layer is not mixed with the tar, but is placed and 
rolled and then coated with tar before placing the 
upper layers. The tar concrete, formed, as above 
described, by mixing hot tar with broken stone, is 
sometimes stored in bins for about three weeks before 
using, to permit the tar to thoroughly saturate the 
stone before placing it in the road. 



l6o A TEXT-BOOK ON ROADS AND PAVEMENTS. 

This method of construction seems to have given 
satisfactory results, and its use is rapidly extending. 
It forms, when well constructed, a smooth, practically 
noiseless pavement, which is easily cleaned and costs 
less to maintain than an ordinary macadam road. 

Tarred Surfaces on Macadam Roads. The applica- 
tion of tar to the surfaces of macadam roads, for the 
purpose of eliminating dust and preventing the ravel- 
ing of the surface, has been found to be efficient and 
economical in many places. This method is largely 
used in France, where it has been employed for several 
years. French engineers who have reported upon 
the matter express the opinion that the cost of main- 
tenance is considerably reduced and the life of the road 
prolonged by such treatment. 

This method is similar to that used in oiling mac- 
adam surfaces and differs considerably in different 
localities. The road must be very dry when the tar is 
applied, and the work should be done during warm, 
dry weather in order to secure the best results. The 
tar will not penetrate properly if the road be damp. 

When an old road is to be treated without resurfac- 
ing, all of the dust should be removed and the surface 
swept clean. The tar is then applied at a temperature 
of about 200 degrees F. and allowed to stand for at 
least 8 or 10 hours, in order to permit the tar to 
penetrate well into the surface of the road. The 
amount of tar used should be only sufficient to form 
a thin coating over the surface of the road, and 
any tar which may collect in low spots in the road- 
surface should be brushed out evenly and* uniformly 
distributed. After sufficient time has elapsed for the 
penetration of the tar, a light layer of stone screen- 
ings or sand is placed over the surface to take up 



BROKEN-STONE ROADS. l6l 

the surplus tar, and the road is rolled with a heavy- 
roller. 

When the surface of the macadam road requires 
repairing and reshaping, the dust is first removed and 
the surface loosened by means of spikes in the wheels 
of the roller. New material is added where necessary 
and the road reshaped and rolled to a hard surface. 
The tar is then applied as in the other case. 

The amount of tar required varies with the character 
of the material composing the road surface; ordinarily 
about one -third gallon to one gallon per square yard of 
road-surface will be required. A second application is 
usually desirable after a year. This second application 
requires less tar. On some of the French roads an 
application of tar is made about once in two years. 
This, it is claimed, is cheaper than sprinkling and 
materially reduces the cost of maintenance. 

The quality of tar varies greatly for this purpose. 
A rather light material which flows readily at the 
temperature of application is required, and it should 
not contain an appreciable quantity of water. On 
account of the difficulty of securing a uniform quality 
of tar, the best results have been obtained with cer- 
tain materials specially prepared for the purpose. A 
preparation known as "tarvia" has been quite exten- 
sively used, most of the successful tarred roads being 
constructed by its use. 

The tar is commonly heated by steam coils in the 
tank cars in which it is shipped, and is distributed upon 
the street in tank wagons which have a small fire-box 
underneath the tank, to keep the tar hot while trans- 
porting it to the street. Various forms of sprinklers 
have been employed for the purpose of spreading the 
tar upon the road, but the best results seem to have 



l62 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

been obtained by the use qf a hose attached to the rear 
of the tank wagon and fitted with a valve for controlling 
the flow, the tar being spread to a width of 12 to 15 
feet as the wagon progresses. Laborers with brooms 
follow the tank and spread the tar evenly over the 
surface. The tar should be spread as evenly and 
quickly as possible, in order that it may be accomplished 
before cooling takes place. Some attempts have been 
made to use tar for this purpose without heating. This 
requires tar light enough to flow readily at ordinary 
air temperatures. There is as yet no experience on 
which to form a judgment concerning the success of 
these lighter materials. 

The coating of screenings upon the surface of the 
road should not be placed until time has been given 
for the tar to penetrate into the road and should only 
be sufficient to cover the surface lightly, so as to dry 
the surface and take up any surplus tar, without 
leaving any residue to be reduced to powder and be 
blown or washed away. 

The cost of treating a road in this manner is compara- 
tively slight, having been in a number of instances 
from 5 to 8 cents per square yard. Experience has 
shown that the surface of a macadam road treated in this 
manner with good materials will not grind up into 
deep dust, and therefore the cost of maintaining is 
reduced and the life of the road prolonged. Such 
roads are likely to come into more general use in the 
future, and to prove economical and desirable for 
country roads and for village and suburban streets of 
light traffic. 

Bituminous Concrete. Tar concrete has, as already 
noted, been quite extensively used in England. This 
construction has been employed to a limited extent in 



BROKEN-STONE ROADS. 1 63 

America, but has not been applied to ordinary road 
work. Bituminous concrete of better grade, using 
carefully graded stone and specially prepared bitumi- 
nous cement, is extensively used under the name of 
"bitulithic pavement." This is discussed in Art. 62. 

Macadam with Asphalt Filler. In several instances, 
roadways have been constructed of macadam the 
surface of which is filled with raw rock asphalt. The 
method of construction employed in these roads is 
to form the macadam surface in the usual manner and 
then, in place of the usual binding material to apply 
a top dressing of ground rock asphalt and roll to a 
smooth surface. 

The asphalt which has been applied to this use is 
Kentucky rock asphalt, containing at least 8 per cent 
bitumen. It is applied in fine condition, without heat, 
and is found to pack firmly under the rolling and traffic, 
the asphalt being forced into the interstices in the 
stone and serving as a binder for the macadam surface. 

It is claimed that the surface of a road formed in this 
manner will not form dust and will not ravel, on account 
of the oily nature of the binder. Some roads con- 
structed in this manner are reported to have given 
satisfactory results for the short time they have 
been in use. These roads are sometimes called by the 
name of the company introducing them, " Wadsworth 
Macadam." 

Oiled Macadam. Gravel and macadam roads are 
constructed in California, using asphaltic oil in much 
the same manner that the tar macadam is used in 
the Eastern states. The following extract from the 
specifications of City Engineer Homer Hamlin for 
graveled streets in Los Angeles shows the method of 
construction employed. 



164 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Surfacing Roadway. "Upon the surface prepared 
and brought to subgrade in the manner above specified, 
shall be spread one layer of good gravel to have a thick- 
ness of 4 inches, unless otherwise shown on the plans, 
profiles or cross sections, after having been rolled. The 
surface of this layer of gravel to a depth of one inch shall 
be raked free from all stones larger than I inch in the 
greatest dimension. If no gutters are provided, these 
larger stones shall be raked to the curb and distributed 
over a strip two feet in width next to the curb. 

" If gutters are provided, then these stones shall 
be distributed on a strip two feet in width next to the 
gutter. This layer of gravel is to be uniformly spread 
on the roadway, and well moistened. The gravel 
shall be well rammed for at least one foot from the 
gutters, should these be paved, or if the gutters are 
not paved, then one foot from the curb. The remaining 
portion of the roadway shall then be rolled with a roller 
weighing not less than 250 pounds to the inch width 
of tire. The rolling of the roadway shall commence 
at the rammed portion. All depressions shall be 
promptly filled, moistened, and again rolled. The 
sprinkling and rolling must be continued until the 
surface is uniformly hard, compact, and in such condi- 
tion that it will not yield or cut up under the wheels 
of a heavily loaded wagon. 

Oiling. "Oil shall then be evenly distributed over 
the entire surface of the roadway, in a volume equal 
to one gallon, by measure, per square yard of surface. 

"Coarse sharp sand shall then be sprinkled over 
the entire surface of the roadway, until no free oil 
can be seen. 

"After a lapse of not less than twelve hours, oil 
shall again be evenly distributed over the entire 



BROKEN-STONE ROADS. 1 65 

surface of the roadway in a volume equal to one-half 
gallon, by measure, per square yard of surface. 

"The entire surface of the roadway shall again be 
sprinkled with coarse sharp sand until the oil is 
completely absorbed, and then rolled with a roller 
weighing not less than 250 pounds to the inch width 
of tire until the surface is unyielding. In all cases 
sufficient sand shall be used to prevent the oiled 
material from picking up. 

"The total amount of oil used shall not be less than 
one and one-half gallons per square yard of the street 
surface. In the process of oiling, care must be taken 
not to soil the curbs or walks. After the oiling of a 
street has commenced it shall be carried on diligently 
and continually to its completion. 

"Sand used for covering the oil must be distributed 
in piles along the sides of the street before the oil is 
applied, and must be spread quickly and in sufficient 
quantity to prevent the oiled surface from picking up. 

"Oil shall not be applied to the surface of a street 
while it is in a wet condition. 

"During and immediately after the rolling, the 
surface of the street shall be gone over with brooms 
or rakes and all irregularities removed." 

The construction of macadam streets in Riverside, 
California, is described by City Engineer A. P. Camp- 
bell as follows : " Prepare the road-bed and make a 
regular macadam pavement. Instead of finishing with 
the ordinary coat of screenings, coat the surface with 
liquid asphalt, about J to f gallon to the square yard, 
then spread about \ inch of screenings over the asphalt 
to act as an absorbent, apply another \ gallon of 
asphalt, coat this again with screenings and roil for 
final. 



1 66 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

"This asphalt surface acts as a waterproof coating 
and prevents the raveling of the surface. 

"You will note that I use the words 'liquid asphalt;' 
that is what our road oil is in fact, and the word oil is 
a misnomer. We specify an oil of ioj Baume, con- 
taining 80 per cent by weight of ' D ' grade asphalt/' 



CHAPTER VI. 

FOUNDATIONS FOR PAVEMENTS. 
Art. 43. Preparation of Road-bed. 

In forming a road-bed upon which to place a pave- 
ment, the earth should be brought at subgrade to the 
form of a finished road-surface, leaving room for the 
superstructure of uniform thickness to be placed upon 
it. Thorough drainage must of course be carefully at- 
tended to when necessary. This has been already dis- 
cussed in Chapter II. 

In the construction of a road-bed to support a 
pavement, the same principles are involved as in the 
earthwork of a common road, which has been discussed 
in Art. 26, and the same methods may be employed 
in handling the earth. In grading, the surface should 
be left high enough to allow for the compression pro- 
duced in rolling. The amount of settling to be ex- 
pected under the roller will vary with the character 
of the material and the weight of the roller. With a 
heavy steam roller, the compression may vary from J 
inch for stiff soil in dry condition to about 3 inches for 
light porous soil. The allowance to be made can only 
be judged from experience with the soil in question. 

The road-bed, after being brought to the proper 
grade, should be thoroughly compacted by rolling 
before placing the pavement. Sometimes in the use of 
a heavy roller, when the material is of a light nature, it 
is shoved forward in a wave before the roller and re- 

167 



1 68 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

fuses to become compacted, in which case a thin layer 
of gravel or small stone placed upon the surface of 
earth before rolling may have the effect of consolidat- 
ing the road-bed under the roller to a hard surface. 

The roller should pass several times over the road- 
bed. When low places are developed, which roll down 
below grade, they should be rilled and rolled again 
until brought to proper grade. Passing the roller trans- 
versely over recently filled trenches will always produce 
depressions which require refilling. Where such trenches 
exist, the rolling should be very carefully done. 

In rolling, soft spots are sometimes discovered, which 
cannot be compacted by rolling. In such cases the 
soft material should be removed and replaced with 
better material to a sufficient depth to admit of roll- 
ing the road-bed to a compact surface. 

In some instances, repeated rolling of light material 
with a heavy roller may have the effect of working the 
material loose so that it moves in a wave before the 
roller, although the first rolling leaves the road-bed 
compact. In such cases it is desirable to avoid too 
much rolling. 

Where much grading is to be done, it is usually de- 
sirable to do the rough work before setting the curb 
upon the street, if a new curb is to be placed. It is, 
however, much easier to finish the grade after the curb 
is set, as a line across the street at the top of the curb 
is a convenient means of getting the elevation of points 
on the sub grade. 

Art. 44. Trenches in Streets. 

The opening of trenches for water, gas, and sewer 
pipes in the streets is perhaps the greatest cause of de- 



■ FOUNDATIONS FOR PAVEMENTS. 1 69 

struction of pavements to be found in the average 
city. This is especially true of the smaller cities, 
where wear from traffic is not excessive. 

In constructing a pavement in an unpaved street 
an effort should always be made to lay all pipes which 
are likely to be needed in the street for a considerable 
period, in so far as they can be foreseen, before placing 
the pavement. Where a cut is made through a pave- 
ment for a trench it is a matter of considerable 
difficulty to backfill the trench and replace the pave- 
ment in as good condition as before it was cut, and 
great care is required to prevent the subsequent set- 
tlement of the pavement over the trench. The filling 
of trenches over which a pavement is to be placed 
requires very close inspection, and frequently, neglect 
of such inspection causes much trouble subse- 
quently. 

The most common method of filling trenches in 
unpaved streets is to throw the earth in loosely, and 
pile the surplus earth in a ridge over the trench, leaving 
it for the natural settlement, when wet weather comes, 
to ultimately compact the earth in the trench. 
Usually, the settlement of such a trench will extend 
over a long period, and there is danger of injury to a 
pavement built over the trench, even after several 
months have elapsed and settlement seems to have 
taken place. Rolling will compact the earth in the 
top of the trench, but its effect does not reach to any 
considerable depth in the trench, or prevent later 
settlement. There are many instances in which 
disastrous settlements of pavements have occurred 
over trenches, although the material in the trenches 
had been considerably settled by rains and the surface 
rolled with a heavy roller. 



170 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Flooding. It is common practice to settle the earth 
in trenches by flooding with water. This is accom- 
plished either by repeatedly filling a few inches of 
earth into the trench and then saturating with water, 
or by flooding the trench with a few inches of water 
and filling the earth into the water. It is difficult to 
compact the earth by flooding so that no further settle- 
ment will take place, and it is necessary to use care that 
the earth be not thrown in in too large quantities at 
once, as when the trench is filled with scrapers or 
graders. When the soil is clay, subsequent settlement 
will take place as the clay shrinks upon drying out. 

In filling sewer trenches in this manner there is 
usually danger of breaking the joints of the sewer in 
flooding the trench. Several instances have been noted 
in which this has occurred, and the practice should 
be avoided. 

Tamping. The only method of effectively compact- 
ing ordinary earth in a trench so that no danger of 
subsequent settlement shall exist is by placing the 
earth in thin layers, not more than 4 or 5 inches 
thick, and tamping each layer thoroughly. To accom- 
plish this the earth must be damp enough to pack well, 
but not too wet. 

The earth compacts into smaller space when rammed 
in the trench than it formerly occupied, so that when 
the pipe is small as compared with the size of the 
trench there may not be enough earth removed in 
excavating the trench to entirely refill it. 

Art. 45. Purpose of Foundation. 

The chief object of the foundation or base of a 
pavement is to distribute the concentrated loads which 



FOUNDATIONS FOR PAVEMENTS. I /I 

come upon the surface of the road over a greater area 
of the usually softer and weaker road-bed, in order 
that these loads may not produce indentations in the 
surface. 

In a foundation composed of independent blocks 
extending through its thickness, as in the case of a 
stone-block pavement in which the blocks rest directly 
upon the road-bed or upon a thin layer of sand, the load 
which comes upon the top of any block will be dis- 
tributed over the area covered by the base of the block. 

Where the foundation is composed of small independ- 
ent particles, like sand or loose rounded gravel, with 
no cohesion through the mass, the pressure is distrib- 
uted over the base of a cone whose vertex is in the 
point of application of the load, and the inclination of 
whose elements depends upon the friction of the par- 
ticles of the material upon each other. In this case 
the area over which the load is distributed varies 
directly as the square of the thickness of the founda- 
tion. Sand, it is to be observed, has also the property, 
when confined as in a foundation, on account of its 
incompressible nature, of adjusting itself to a uniform 
pressure and resisting the deformation of the road-bed. 
If the small pieces composing the foundation are 
cemented together, or held as in masses of angular 
fragments by the interlocking of the angles, the foun- 
dation may act more or less as a whole, causing a distri- 
bution of the load over a considerable area, the extent 
of which will depend upon the resistance of the mass 
to bending. 

The bases most commonly employed for pavements 
are sand, broken stone, and concrete. Foundations of 
brick and wood are also sometimes employed for pave- 
ments of the same materials. 



I ?2 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 46. Bases of Gravel and Broken Stone. 

For light service on a good road-bed a satisfactory 
foundation may frequently be constructed of gravel 
or broken stone at much less expense than would be 
required for a concrete base. A foundation of this 
character should be constructed in about the same 
manner as a broken-stone road, the material being 
spread over the road-bed and thoroughly rolled to 
the required form. The stone or gravel employed 
should contain sufficient small material to fill the 
voids in the aggregate, or a binding material may be 
added to aid in compacting the foundation, and to 
close the interstices so as to prevent any settling of 
the material which is used to support the paving 
surface. 

These foundations are sometimes used under brick 
pavements of light traffic with good results. It is 
important, in the construction of brick pavements in 
this manner, that the interstices in the base be thor- 
oughly filled; as otherwise the sand cushion under the 
bricks may gradually settle into the foundation. 

A foundation of this kind can never have the strength 
and permanence of a concrete base, and, while they 
may give good results when well constructed under 
proper conditions, they have frequently been used 
where a small additional expense for concrete would 
have been much more economical in the end. 

Art. 47. Concrete Bases. 

The best base for general use under pavements is 
without doubt that formed of hydraulic cement con- 
crete. A bed of concrete made of good hydraulic 



FOUNDATIONS FOR PAVEMENTS. 1 73 

cement, well rammed and allowed to set and harden, 
becomes a practically monolithic structure, nearly im- 
pervious to water and possessing a high degree of 
strength against crushing. 

The concrete is formed of a mixture of cement, 
sand, and broken stone or gravel. The proportions 
vary for different work and with the character of the 
materials. With good Portland cement the most 
common proportions for ordinary work are about one 
part cement, 3 parts sand, and 5 to 7 parts broken 
stone. With the various natural cements the pro- 
portions vary somewhat, but are usually about I part 
cement, 2 parts sand, and 4 or 5 parts of stone or 
gravel. 

Natural cement is usually employed for this pur- 
pose as being cheaper and possessing ample strength 
for the work, and concrete of the ordinary propor- 
tions with natural cement is to be preferred to that 
made with meager proportions of Portland cement 
giving about the same strength and cost. Proper tests 
should always be imposed for the purpose of securing 
good cement.* 

Sand for use in mortar should be as clean and as 
free from loam, mud, or organic matter as possible. 
In general the presence of any foreign matter is to be 
avoided. Coarse sand is usually preferable to that 
which is very fine, provided it be line enough to give a 
smooth mortar, as it affords better strength. The use 
of a mixture of grains of various sizes is usually desirable 
as giving less voids to be filled by the cement. 

The aggregate used for concrete should be as hard 

* For discussion of tests of cement see "Hydraulic Cement, its Prop- 
erties, Testing and Use," by F. P. Spalding. John Wiley and Sons, 
New York. 



1^4 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and durable as possible, and that of angular form is 
preferable to rounded. The materials should be uni- 
form in quality. When gravel is used which varies in 
quality, it should be blended by mixing in order to 
obtain uniform strength in the concrete. The best 
concrete will usually be made from the stone contain- 
ing the smallest percentage of voids, provided the 
material be uniform. In a mass of ordinary broken 
stone the voids are usually from 40 per cent to 55 per 
cent of the volume. This may be considerably reduced 
by careful adjustment of the sizes. The broken stone is 
commonly limited in size to 2 or 2 J inches, and the 
whole output of the crusher is used, with the dust 
screened out. The quantity of sand needed is such as 
will fill the voids in the aggregate. 

In preparing the concrete, the cement and sand 
should first be thoroughly mixed while dry, then the 
proper quantity of water be added all at once, and 
the mortar be vigorously worked with hoe or shovel 
for 2 or 3 minutes, until it comes to a smooth and uni- 
form condition. 

The quantity of water should be such as under 
energetic working will reduce the mortar to a soft, 
plastic condition, and should be determined by meas- 
ure. The application of the water from a hose during 
the mixing is objectionable on account of the diffi- 
culty of regulating the quantity to produce mortar of 
proper consistency. 

When the mixing of the mortar is complete, the 
stone or gravel may be added, and the whole mass 
turned several times with shovels until the mortar is 
evenly distributed through the aggregate. The stone 
should be wet by sprinkling before it is mixed with 
the mortar, in order to clean the surfaces of dust and 



FOUNDATIONS FOR PAVEMENTS. 1 75 

to prevent the absorption of water from the mortar 
before it sets. 

The concrete, when ready, is placed in position and 
tamped to surface. For this use it is preferable that 
the concrete be of jelly-like consistency, such that it 
will quake under light ramming. The rammer com- 
monly employed consists of a block of wood, or of cast 
iron, 6 to 8 inches square, flat on the bottom, and 
weighing 20 to 30 pounds. The tamping should cause 
the mortar to flush to the surface. 

After completion the foundation should be allowed 
to stand several days before the pavement is placed 
upon it, — 3 to 6 days are usually required, — in order 
that, the mortar may become entirely set. During 
setting the concrete should be protected from the 
drying action of the sun and wind, and should be kept 
damp to prevent the formation of drying cracks. 

The quantity of material necessary to make a cubic 
yard of concrete varies with the density of the broken 
stone. For materials measured loose, to make a cubic 
yard of 1, 2, 4 concrete will require ij to I J barrels of 
natural cement, T 4 ff to T 5 o cubic yard of sand, and T 8 7 to 
I cubic yard of broken stone. To make 1 cubic yard of 
I, 3, 6 concrete requires T 8 o to I barrel of Portland 
cement, T 4 ff to T 5 o cubic yard of sand, and T % to I cubic 
yard of broken stone. 

Art. 48. Bituminous Foundations.. 

Foundations of bituminous concrete are frequently 
used under asphalt and bitulithic pavements, and, in 
some instances, under other surfaces. These founda- 
tions are constructed in much the same way as bitu- 
minous macadam roads (see Art. 42). In some 



I 76 A TEXT-BOOK ON ROADS AND PAVEMENTS, 

instances the bases are formed of concrete composed 
of broken stone and tar, or asphalt cement mixed in 
the same manner as the binder course for an asphalt 
pavement (see Art. 58), and rolling or tamping the 
concrete into place. 

The more common method of construction is by 
spreading and rolling the broken stone, 4 or 6 inches 
thick, as for a macadam road, and covering the surface 
with a coating of bituminous cement. Coal-tar cement 
is ordinarily used for this purpose, or a mixture of coal- 
tar and asphalt. 

The bituminous foundation is commonly employed 
in the construction of bitulithic pavements (see Art. 62) . 
The advantage claimed for it is that it permits the over- 
lying courses to bind into the foundation and holds 
the surface layer in place. Foundations of this kind 
give good results when the road-bed is firm, so that it 
may be rolled solid and is not likely to become unstable. 
It has not, however, the stability of hydraulic cement 
concrete and should not be used where strength is 
needed or where the road-bed is composed of spongy 
clay or other material which cannot be rolled to pro- 
vide a solid sub -foundation. 

Art. 49. Miscellaneous Foundations. 

Brick Foundations. Foundations of brick have fre- 
quently been used under brick pavements. The pave- 
ment in such cases consists of two layers of brick, with 
sand between, and is known as double-layer pavement. 
These foundations are usually formed by placing upon 
the road-bed a layer of sand or gravel 3 or 4 inches thick, 
which is rolled thoroughly to a uniform surface, and 
then receives a layer of brick, commonly laid flat and 



FOUNDATIONS FOR PAVEMENTS. 1 77 

with the greatest dimension lengthwise of the street. 
These bricks are laid as closely as possible with 
broken joints. The joints are filled with sand care- 
fully swept in, and the bricks are rammed to a firm 
bearing. 

Upon this course of brick is placed a cushion layer 
of sand, and then the surface layer. The bricks of the 
lower layer may be of a cheaper grade than the sur- 
face paving brick, as they are not required to resist the 
attrition of travel. 

Care must be used to thoroughly fill the joints in the 
foundation layer of brick in order that the sand in the 
cushion layer may not work downward and allow 
the surface bricks to settle. 

These foundations were formerly quite extensively 
used for brick pavements, but have for the most part 
been superseded by concrete or macadam bases. They 
have, in many instances, given good results in use 
when resting upon a firm road-bed, but lack the 
strength of the concrete foundation and are not usually 
economical. 

Sand and Plank Foundation. Under many wood 
pavements, and sometimes under brick surfaces, foun- 
dations formed of sand and planks have been used. 
These foundations differ somewhat in construction in 
various localities, but are essentially a bed of sand or 
gravel, upon which is placed a layer of tarred boards 
which support the surface layer. 

It is common to use a layer of sand 3 or 4 inches 
thick, which is compacted by rolling, after which the 
boards are laid lengthwise of the street close together, 
so as to form a floor upon which the blocks may be 
set. With a brick surface a cushion coat of sand is 
used under the surface layer. 



178 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Sometimes two layers of one-inch tarred boards are 
employed, the lower being laid crosswise of the street 
and the upper lengthwise of it. In other cases the 
boards of a single thickness are nailed to scantling laid 
across the street and bedded in the sand. The boards 
must in all cases press evenly upon the layer of sand 
that covers the road-bed. 

These foundations were used under the round block- 
wood pavement, at one time quite extensively. They 
are employed only where low cost of construction is 
necessary, and are not economical when a durable road- 
surface is to be constructed. 

Sand Foundations. Brick pavements have frequently 
been constructed with only a cushion coat of sand upon 
the earth road-bed. In some instances, where the 
road-bed is firm and well drained, forming a natural 
foundation, this method of construction has been 
successful under light traffic, but the failures have been 
numerous, and it is only under exceptional circum- 
stances that such construction will prove economical. 
The same method has been applied to wood-block and 
stone-block pavements, stone blocks being usually set 
in a bed of sand or gravel 4 to 8 inches deep. 

Art. 50. Choice of Foundation. 

It is always important that the foundation be suffi- 
cient. The yielding of the base of the pavement means 
its destruction. 

If a firm and durable foundation be employed, the 
surface may be renewed when necessary or changed 
from one material to another without disturbing the 
base, but if the base be weak the surface will be 
destroyed. 



FOUNDATIONS FOR PAVEMENTS. 1 79 

The saving of expense should be at the top rather 
than at the bottom of a pavement. 

The thickness required for the foundation of a pave- 
ment depends upon the nature of the soil upon which 
it is to rest, and upon the extent and weight of the 
travel to which it is to be subjected. 

When the road-bed is of a retentive material and 
likely to become wet and soft, the foundation should 
possess sufficient strength not to be broken through at 
points where the supporting power of the road-bed may 
be destroyed by water. It must also be able to resist 
the action of frost upon the soil below. In such cases 
8 or 9 inches of concrete may be necessary. Six inches 
of good concrete, however, constitute a foundation of 
considerable strength, and it is only under severe con- 
ditions, poor support and heavy traffic, that a greater 
depth is necessary. 

Under light traffic with good conditions, a less depth 
may be sometimes used; 4 inches of concrete is fre- 
quently employed to save expense, although 6 is the 
more common depth. A depth of 4 or 6 inches of well 
compacted gravel or broken stone is also usually suffi- 
cient where the conditions are such as to admit of the 
use of a foundation of that character. 

It may be here observed that no definite prescrip- 
tion for any pavement, either as to choice of founda- 
tion or as to methods of construction, can fit all cases. 
What is most successful in one case is quite inappli- 
cable in another. The blind following of particular 
rules by those not conversant with the principles upon 
which they are based has been the cause of many fail- 
ures. Judgment must always be used in weighing the 
local conditions of the problem in hand. 



CHAPTER VII. . 

BRICK PAVEMENTS. 
Art. 51. Paving-brick. 

The requisites for a good paving-brick are that it 
shall be hard, tough, and impervious, as well as capable 
of enduring against the disintegrating influences of the 
weather. 

The bricks in most common use are made from fire- 
clay of an inferior quality, or from an indurated clay or 
shale of somewhat similar composition. 

These clays consist essentially of silicate of alumina, 
with usually small percentages of lime, magnesia, iron, 
potash, soda, and sometimes other elements. The 
range of composition for clays in common use is 
approximately as follows: 

Per cent . 

Silica 60 to 75 

Alumina 10 to 25 

Iron oxide 3 to 8 

Lime to 4 

Magnesia to 3 

Potash 0.5 to 3 

Soda to 2 

In a few cases the quantity of lime is greater, vary- 
ing from 8 to 12 per cent. 

When the clay is very nearly pure silicate of alumina, 
it is capable of withstanding a high degree of heat 
without fusing, and is known as fire-clay. As the per- 

180 



BRICK PAVEMENTS. l8l 

centages of other ingredients increase, it becomes more 
fusible. The lime, magnesia, potash, and soda act as 
fluxing agents, and the readiness with which the clay 
can be melted depends upon the relative quantities of 
refractory and fluxing materials that it may contain. 

Silica in excess tends to make the brick weak and 
brittle, while too great quantity of alumina causes the 
brick to crack and warp in the shrinking which occurs 
during burning. The proper adjustment of the rela- 
tions between these elements is necessary to good 
results. 

The quantity of lime in the clay is an important 
matter, as the presence of lime in an uncombined state 
in the brick may be productive of disintegration when 
the brick is exposed to the weather. A large percent- 
age of lime in a clay is therefore to be regarded with 
suspicion, although not necessarily as cause for con- 
demnation, as its effect depends upon the state of com- 
bination of the various ingredients of the brick. Mag- 
nesia probably acts in much the same manner as lime. 
Potash and soda are considered desirable elements in 
quantities to properly flux the clay in burning. 

The fineness of a clay is also a matter of importance, 
both because a fine clay will fuse at a lower tempera- 
ture than a coarse one, and because fineness is neces- 
sary to the production of even and close grained brick, 
and therefore conduces to make them tough and 
impervious. 

To produce a good paving-brick, a clay is required 
which will vitrify at a high heat. A very refractory 
clay will make a porous brick, while if it melts at too 
low a temperature it cannot be burned sufficiently to 
become hard and tough, 

The methods of manufacturing paving- brick vary in 



1 82 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

different localities according to the character of the 
material to be worked. They are quite similar to 
those in use for common brick, only more thoroughly 
executed. 

The clay is commonly reduced to a fine powder, 
tempered with water and passed through a machine 
that molds the bricks, which are then dried and after- 
ward burned. Repressed bricks are those which are 
compressed in a mold after coming from the brick 
machine and before drying. 

The process of burning occupies usually from 10 to 
15 days. 

The heat is at first slowly applied to expel the water, 
then raised to a high temperature for several days, 
after which the bricks are very slowly cooled. 

There is considerable difference of opinion among 
engineers and manufacturers as to the exact amount of 
burning necessary. It is usually stated that the brick 
should be burned to the point of vitrification, but not 
completely vitrified. The burning must be thoroughly 
done to produce a strong and impervious brick, but 
there is undoubtedly a point beyond which, for some 
brick, further burning causes brittleness. Very gradual 
cooling is also necessary in order to toughen the brick. 
Smoothness and uniformity of texture in a paving 
brick is an important consideration as affecting its re- 
sistance both to crushing and to abrasion. The broken 
surface of the brick should present a uniform appear- 
ance both in texture and in color. 

All the^ bricks used in the same pavement should 
also be of the same degree of hardness and toughness 
in order that the pavement may wear evenly, and to 
this end careful inspection should always be given to 
the bricks proposed for use, and all of those which are 



BRICK PAVEMENTS. 183 

defective, soft from imperfect burning, brittle from 
overburning or quick cooling, cracked or distorted by 
unequal shrinkage, should be rejected. An examina- 
tion of the color and size of the bricks may frequently 
be useful in determining for any particular material 
whether individual bricks have received the proper 
degree of burning, after the engineer has become 
familiar with the make of brick under examination. 
The amount of shrinkage in burning is often a quite 
reliable index of the degree of burning to which the 
material has been subjected, and specifying within 
somewhat narrow limits the variation in size of bricks 
to be used together may often conduce to greater 
uniformity in the material employed. Some makes of 
brick vary quite appreciably in size for small differ- 
ences in extent of burning, and without materially 
affecting the value of the product, but it is desirable 
to sort them closely and use those of each size by 
themselves. 

The mistake is frequently made of placing too high 
value upon the element of hardness, which when car- 
ried to an extreme is sometimes attained at the ex- 
pense of toughness, the brick becoming brittle and 
easily shattered. The author (under his guaranty 
on a pavement) has, on one occasion, been obliged to 
replace a small number of hard bricks, which at the 
time of laying were supposed to be among the best 
of the lot, on account of their becoming shattered under 
traffic, while somewhat softer brick from the same kilns, 
the use of which was questioned by the inspector, 
proved guite satisfactory in the same work. 

The sizes of paving-bricks vary considerably as 
made by different manufacturers, the most common 
sizes approximating to those of building brick, varying 



1 84 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

from about 2\ to 2-| inches in width, 8 to 8 J inches 
long, and 4 inches deep, about 56 to 63 bricks being 
required for a square yard of pavement. A few 
makers also produce a brick, of about the same size 
but only 3^ inches deep. A larger size, usually about 
3X9X4 inches, and known as a paving-block to 
distinguish it from the smaller brick, is quite largely 
employed. These usually require from 43 to 47 
blocks per square yard. 

Larger blocks have been tried, but have not come 
into general use, while some manufacturers make 
smaller sizes, requiring 70 to 75 bricks to the square 
yard of pavement. 

Opinions differ as to the best sizes for use in pave- 
ments, some engineers specifying the smaller bricks, 
others the larger blocks. A good pavement can 
be built of either if proper attention be given to 
selecting the material. The sizes preferred by the 
various manufacturers depend largely upon the 
character of the clay or shale with which they have to 
deal. With some materials the size is limited by the 
distortion of large blocks in burning, and the smaller 
bricks are preferable; with others, larger blocks may 
be made at less cost in proportion to area of pavement, 
and perhaps with better and smoother work resulting. 
There seems to be no necessity for any increase in the 
usual depth of 4 inches as is sometimes proposed, and 
it may be possible that the adoption of the depth, 3^ 
inches, now frequently used may in many instances 
somewhat lessen the cost of the pavement without 
affecting its length of service. 

Much difference of opinion has been developed 
among engineers as to the advisability of rounding the 
corners of the brick, some requiring that the blocks be 



BRICK PAVEMENTS. 1 85 

repressed with corners rounded to a radius of } 01 J of 
an inch, while others specify square-edge brick, and 
in some instances that they shall not be repressed. 
On the one hand, it is maintained that in service the 
sharp corners will soon be knocked off and worn 
down more roughly and unevenly than if originally 
rounded, while, on the other hand, it is claimed 
that if a rigid filler like Portland cement be used, the 
joint may be filled level with the surface of the brick, 
and be much less likely to chip out than if the joint 
be widened at the top so as to cause the filler to pre- 
sent a thin edge at the sides. Both contentions seem 
reasonable under certain conditions, and the method 
of construction and character of filler used will ordi- 
narily determine the proper form for the brick. 

The desirability of repressing the brick is also a 
much discussed question, it being argued by some that 
the repressing of the material forms a more dense and 
compact block and increases its probable wear in use, 
and by others that the pressure applied to the material 
after it comes from the brick-machine disturbs the 
structure and injures the fiber of the brick, often 
forming laminations which are elements of weakness. 
With some materials this last contention seems to 
have some basis in fact, but in other and probably 
most materials no such condition can be found on 
examination of the structure of the brick. The views 
of individual manufacturers upon the question seem to 
depend mainly upon the kind of material they have 
to work with, and it would be difficult from existing 
data to say that either method necessarily gives the 
best results. Possibly those materials which approach 
most nearly to actual vitrification and are subject to 
considerable shrinkage during the burning are but 



1 86 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

little affected in final density by the compression of 
the block before burning. It should be observed in 
this connection that whatever may be the value of 
repressing as to its effect upon the quality of the brick 
and wear of the pavement, it undoubtedly has the 
effect with some kinds of brick of giving a smoother 
and better surface to the pavement by producing a 
more regular and uniformly shaped brick. 

In order to give sufficient space between the bricks 
for the joint-filling, some manufacturers make re- 
pressed bricks with lugs on one side to hold them a 
given distance apart when laid in the pavement. The 
wisdom of this under ordinary circumstances seems 
doubtful, as small joint-space is usually desirable, and 
experience shows that bricks laid close, even if care- 
fully driven up, will usually give plenty of space for 
filling. Spacing-lugs are seldom required in specifica- 
tions, but engineers have sometimes required their use 
for work on steep grades with the idea of giving 
better foothold to horses than the thin joints would 
afford. There may be some advantage in this, and 
some pavements so constructed on grades of above 
eight per cent have given satisfactory results, the lugs 
usually projecting about half an inch from the face of 
the brick, but in the author's own experience he has 
been unable to notice any difference in the use of the 
pavement with or without the wide joints, all being 
laid with bevel-edge brick. 

Repressed bricks and blocks are frequently made 
with a groove or two, extending lengthwise of the 
brick on each side and sometimes across the ends, for 
the purpose of keying the blocks together when filled 
with the joint -filler. This may be an aid to rigid 
construction, though not necessary to good work. 



BRICK PAVEMENTS. 187 

It is usually limited to the larger blocks, which fre- 
quently have thin lugs, as well as the grooves, and 
are known as groove- and lug-blocks. They are well 
calculated to give a very firm construction. 

Art. 52. Tests for Paving-brick. 

To determine the probable durability of brick 
designed for use in paving, mechanical tests may be 
applied which will show the relative rank of different 
samples in their most important characteristics. It is, 
however, a matter of considerable difficulty to set a 
standard to which the brick should be required to con- 
form, or to determine, from the behavior of the bricks 
under test, the relative value of various samples which 
it may be desired to compare. 

The tests ordinarily proposed or used for this purpose 
are those of crushing strength, transverse strength, 
abrasion and impact, absorption, and specific gravity. 
The relative importance of these tests and the weight 
which should be given to their results is a matter 
concerning which considerable difference of opinion has 
been developed amongst engineers, and practice va- 
ries considerably. The National Brick Manufacturers' 
Association have considered the matter, and in 1895 
appointed a committee which in 1897 reported a set 
of rules for making the tests, with resolutions expressing 
their views as to the relative importance and reliability 
of each. These rules, which were somewhat modified 
in 1900, are very commonly followed and furnish a 
standard method of testing. 



1 88 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

CRUSHING TEST. 

The recommendations of the commission for con- 
ducting this test are as follows: 

"I. The crushing test should be made on half- 
bricks, loaded edgewise, or as they are laid in the 
street. If the machine used is unable to crush a full 
half-brick, the area may be reduced by chipping off, 
keeping the form of the piece to be tested as nearly 
prismatic as possible. A machine of at least 100,000 
pounds capacity should be used, and the specimen 
should not be reduced below 4 square inches of area 
in cross-section at right angles to direction of load. 

"II. The upper and lower surfaces should prefer- 
ably be ground to true and parallel planes. If this is 
not done, they should be bedded in plaster of Paris 
while in the testing-machine, which should be allowed 
to harden ten minutes under the weight of the crush- 
ing planes only before the load is applied. 

"III. The load should be applied at a uniform rate 
of increase to the point of rupture. 

"IV. Not less than an average obtained from 5 
tests, on 5 different bricks, shall constitute a stand- 
ard test." 

The result of a compressive test of stone or brick 
depends very largely upon how it is made, and the 
results of tests are only properly comparable with 
others made in the same manner and with equal care. 
The use of plaster beds as suggested above, it is 
thought, conduces greatly to regularity of result in the 
work of different men, as it tends to reduce the effect 
of differences in the accuracy of dressing the surfaces 
of contact. The size of the test-piece is also impor- 
tant, the strength usually increasing as the size in- 



BRICK PAVEMENTS. 1 89 

creases. Small pieces, I \- or 2-inch cubes, are often 
employed because of the large force necessary to crush 
a whole or half brick, although where machinery exists 
capable of doing it the larger tests entail much less 
work in preparing specimens and also yield much 
more satisfactory results. Where small specimens are 
used it is to be observed that the unit strength will 
not be the same as for larger ones, and must be judged 
by a different standard. In the preparation of speci- 
mens it is better, when possible, to saw than to break 
them by chipping, in order not to injure the block by 
the shock of the blows. 

The commission in their discussion concluded that 
no connection has been shown between high strength 
and the qualities necessary for a good paving material, 
and adopted the following resolution: 

"Whereas, From the experimental work done so 
far by this commission, or by others so far as is known 
to us, in the application of the cross-breaking and 
crushing tests to paving-bricks, it is not possible to 
show any close relationship between the qualities 
necessary for a good paving material and high struc- 
tural strength as indicated by either of these tests, 

"Resolved, That for this reason the commission rec- 
ommends that these tests shall be considered as purely 
optional in the examination of paving material, and 
not necessary as a proof of excellence/* 

It is to be observed that the actual crushing strength 
of a brick is not a matter of special importance in so 
far as any danger of the crushing of the material in the 
pavement is concerned, as no stress can there come 
upon it under ordinary circumstances which would 
endanger even a very weak specimen from direct 
crushing. It is thought, however, that to some extent 



190 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the value of the brick is indicated by its resistance to 
crushing, coupled, of course, with a proper examina- 
tion of its other necessary attributes. A brick which 
possesses a high crushing strength is not necessarily 
a good paving-brick, as it may at the same time be 
brittle or of such composition as to easily disintegrate 
under the action of the weather; but one that yields 
to a low crushing strength is usually weak in wearing 
qualities and not fit for the purpose. For this reason 
this test is commonly included in specifications pre- 
scribing tests, although it is recognized that the rela- 
tive wearing qualities of various makes of brick can- 
not be graded by its results. A good paving-brick, 
in the form of a 2-inch cube, will usually show a re- 
sistance to crushing of not less than 10,000 pounds 
per square inch. Much higher values are sometimes 
used in specifications, but their advantage is at least 
doubtful. 

TRANSVERSE TEST. 

The transverse strength is tested by supporting the 
brick upon two knife-edges near its ends and bringing 
a load through a third knife-edge upon the middle of 
the brick. The test may be made upon any ordinary 
testing-machine by providing the necessary knife- 
edges, but, like the compression test, requires care in 
manipulation to get good results. It is specially im- 
portant that the brick have a perfectly even bearing 
upon the supports before the application of the load, 
in order that it may not be subjected to a twist under 
the load. The method adopted by the commission 
for this test is as follows : 

I. Support the brick on edge, or as laid in the 
pavement, on hardened steel knife-edges rounded 



BRICK PAVEMENTS. 191 

longitudinally to a radius of 12 inches and trans- 
versely to a radius of one-eighth inch, and bolted in 
position so as to secure a span of six inches. 

II. Apply the load to the middle of the top face 
through a hardened steel knife-edge, straight longi- 
tudinally and rounded transversely to a radius of one- 
sixteenth inch. 

III. Apply the load at a uniform rate of increase 
till fracture ensues. 

IV. Compute the modulus of rupture by the for- 
mula 

,3 wl 



2 bd 2 

in which / = modulus of rupture in pounds per square 
inch; 
w = total breaking load in pounds; 
/ = length of span in inches = 6; 
b = breadth of brick in inches; 
d = depth of brick in inches. 

V. Samples for test must be free from all visible 
irregularities of surface or deformities of shape, and 
their upper and lower faces must be practically parallel. 

VI. Not less than 10 brick shall be broken and the 
average of all be taken for a standard test. 

The commission included this test with the crush- 
ing test in the recommendation that the test was to 
be considered optional and "not necessary as a proof 
of excellence. " This test is easier to conduct satis« 
factorily, and probably gives, in general, a more reli- 
able indication of the value of the material than the 
crushing test. It calls into play the tensile as well 
as compressive strength of the brick. The interior 
structure is shown by the break, and an opportunity is 



192 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

given to judge of the uniformity and homogeneous 
character of the material. 

The fracture of a tough and homogeneous speci- 
men under a transverse load should be a clean break 
through the middle of the brick, and a close observa- 
tion of the breaks may frequently be of considerable 
assistance in forming an idea of these qualities, al- 
though they may not be directly represented by the 
load required to break the specimen. The shattering 
of the brick in breaking, or an irregular break extend- 
ing from the point of application of the load to one 
of the points of support, usually indicates brittleness 
of the material. 

The modulus of rupture of good paving-bricks 
commonly ranges between 2000 and 3000 pounds per 
square inch, sometimes reaching 3500 or even 4000 
pounds. It is usually somewhat greater for brick laid 
flat than for brick on edge. 

ABRASION TEST. 

In the convention of 1897 the Brick Manufacturers' 
Association adopted a method for this test consisting 
in rattling a given charge of bricks in a cylinder rotat- 
ing about its axis, which is horizontal, and depending 
for its result upon the impact and abrasion of the 
bricks upon each other. In 1900, however, after 
more fully considering the matter, the test was modi- 
fied, and a smaller charge of bricks, with the addition 
of a charge of cast-iron shot, was recommended as 
more nearly representing the conditions of practice 
and giving results more in accord with experience. 

The method finally recommended by the Associa- 
tion is as follows: 



BRICK PAVEMENTS. 1 93 

"I. Dimensions of the Machine. The standard 
machine shall be 28 inches in diameter and 20 inches 
in length, measured inside the rattling-chamber. 

"Other machines may be used varying in diameter 
between 26 and 30 inches, and in length from 18 to 
24 inches; but if this is done, a record of it must be 
attached to official report. Long rattlers may be cut 
up into sections of suitable length by the insertion of 
an iron diaphragm at the proper point. 

"II. Construction of the Machine. The barrel shall 
be supported on trunnions at either end; in no 
case shall a shaft pass through the rattling-chamber. 
The cross-section of the barrel shall be a regular 
polygon having 14 sides. The heads and staves 
shall be composed of gray cast iron, not chilled or 
case-hardened. There shall be a space of one-fourth 
of an inch between the staves for the escape of dust 
and small pieces of waste. Other machines may be 
used having from 12 to 16 staves, with openings 
from one-eighth to three-eighths of an inch between 
staves; but if this is done, a record of it must be 
attached to the official report of the test. 

"777. Composition of the Charge. All tests must 
be executed on charges containing but one make of 
brick or block at a time. The charge shall consist of 
9 paving-blocks or 12 paving-bricks, together with 
300 pounds of shot made of ordinary machinery cast 
iron. This shot shall be of two sizes, as described 
below, and the shot-charge shall be composed of one- 
fourth (75 pounds) of the larger size and three-fourths 
(225 pounds) of the smaller size. 

"IV. Size of the Shot. The larger size shall weigh 
about 7 i pounds and be about 2 \ inches square and 
4i inches long, with slightly rounded edges. The 



194 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

smaller size shall be cubes of I i inches on a side, with 
rounded edges. The individual shot shall be replaced 
by new ones when they have lost one-tenth of their 
original weight. 

" V. Revolutions of the Charge. The number of 
revolutions of a standard test shall be 1800, and the 
speed of rotation shall not fall below 28 nor exceed 
30 per minute. The belt -power shall be sufficient to 
rotate the rattler at the same speed whether charged 
or empty. 

" VI. Condition of the Charge. The bricks com- 
posing the charge shall be dry and clean and as 
nearly as may be possible in the condition in which 
they were drawn from the kiln. 

" VII. Calculation of the Result. The loss shall 
be Calculated in the per cents of the weight of the 
dry brick composing the charge, and no result shall 
be considered as official unless it is the average of two 
distinct and complete tests made on separate charges 
of brick." 

The commission regard this as the most important 
test to be applied to paving-brick, and in fact it is 
the only one having their indorsement. It seems 
reasonable to suppose that this test gives more nearly 
than the others a determination of the value of the 
brick for use in a pavement. 

It is quite true that the action to which the brick 
is subjected in a test of this character is different 
from the wear to which it is subjected when firmly 
held in the pavement, but the qualities necessary to 
resist wear in the two cases are very similar. We 
may form an idea of whether a material is suitable for 
the proposed use from such experiments, although no 
definite idea of the amount of wear that it will en- 



BRICK PAVEMENTS. 195 

dure can be obtained from them. It should also be 
pointed out that the method of estimating the loss of 
the brick, from abrasion tests made in this manner, as 
percentages of the total weight of brick, can, in the 
comparison of different bricks, only give correct re- 
sults when the bricks compared are of the same size 
and shape. A brick with rounded edges evidently 
could not properly be compared with one with sharp 
edges by this method, and some engineers have divided 
the test into two periods for the purpose of separat- 
ing the knocking off of the corners and preliminary 
rounding of the brick from the later abrasion upon 
the rounded surfaces which would be more nearly 
comparable for different specimens. If, in the test, 
•the loss in the rattler during the first half-hour be 
separated from that during the second half-hour, 
the latter will be found to be much less affected by the 
form of the brick. 

In comparing bricks of different sizes it should be 
noted that a small brick presents more surface for 
abrasion than a large one in proportion to its volume, 
and the results of such comparisons would be con- 
siderably modified in some instances if the results be 
stated in terms of exposed surface instead of percent- 
age of volume. With square-edged brick during the 
early period of the test, when corners are being 
chipped off, the loss is probably more nearly propor- 
tional to length of edges than to surface or volume, 
which would be still more to the disadvantage of the 
small brick. Care is therefore necessary in drawing 
conclusions from such tests concerning the relative 
values of different materials that all the conditions 
which may affect such conclusions be fully under- 
stood. 



I96 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

A rattler for testing paving-brick has been patented 
by Mr. Gomer Jones, formerly City Engineer of 
Geneva, N. Y., in which the brick are held in the 
circumference of the rattler, and a charge of 150 
pounds of cast-iron cubes, ij inches on the edge, is 
placed in the rattler and revolved. The machine is 
the ordinary rattler, 24 inches in diameter, with staves 
made to clamp the brick end to end, leaving the brick 
exposed about one inch in depth on the side. The 
action is that of picking and abrading the surface 
by light blows, and is claimed to develop the defects 
and pick out soft spots in the brick much better than 
the ordinary method, and avoid breaking the brick by 
heavy blows. The treatment given by this apparatus 
is certainly more like the conditions under which the 
brick is used in the pavement than that given by the 
standard method. 

ABSORPTION TEST. 

This test is made by weighing the specimen dry, 
then saturating it with water, weighing again, and 
stating the absorption as a percentage of the dry 
weight. The Commission of the Brick Manufacturers' 
Association oppose the use of this test, but recommend 
the following procedure for the test when used: 

I. The number of bricks for a standard test shall 
be 5. 

II. The test must be conducted on rattled bricks. 
If none such are available, the whole bricks must be 
broken in halves before treatment. 

III. Dry the bricks for 48 hours at a temperature 
ranging from 230 degrees to 250 degrees F. before 
weighing for the initial dry weight. 



BRICK PAVEMENTS. 1 97 

IV. Soak for 48 hours, completely immersing the 
brick. 

V. After soaking and before reweighing wipe the 
brick until free from surplus water and practically 
dry on the surface. 

VI. Re weigh the samples at once on scales which 
are sensitive to I gram. 

VII. The increase in weight due to absorption is to 
be calculated in percentage of the dry weight of the 
original bricks. 

The commission also adopted the following resolu- 
tion : 

"Resolved, That, in the opinion of the commission, 
any paving-brick which will satisfy the requirements 
of reasonable mechanical tests will not absorb sufficient 
water to prove injurious to it in service. We therefore 
recommend that the absorption test be abandoned as 
unnecessary, if not actually misleading." 

The purpose of this test, when made, is to insure 
the proper burning of the brick to a compact and non- 
absorbent structure. It is probable, as claimed by the 
commission, that these qualities will always be shown 
by the other tests, and that this one is not of very 
great importance, but in many instances it may give 
useful information. A good paving-brick will not 
usually absorb more than 4 per cent or 5 per cent of 
water, but the amount of absorption depends largely 
upon the nature of the material from which the brick 
is made. Many of the shale bricks absorb less than 
I per cent of water if properly burned, while some ot 
the so-called fire-clay bricks when of equally good 
quality will absorb 3 per cent or 4 per cent. A 
specification which would insure the proper burning 
of the one class would exclude the best of the other 



I98 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

class. A limit to the amount of absorption allowable 
is, however, commonly set in specifications. 

The requirement of drying 48 hours is probably, in 
most instances, sufficient and reduces the moisture in 
the brick so that the further loss from continued 
drying would be very slight, but the saturation of the 
brick will not usually be accomplished by immersing 
for 48 hours. Some bricks will in that time have 
taken up but a small part of the water they would 
finally absorb, and much longer time would be neces- 
sary to give a complete indication in this particular. 
Some experiments by Mr. Harrington of St. Louis, 
the results of which were presented to the Brick 
Manufacturers' Association, showed a considerable 
change in the quantity of water absorbed by some 
bricks through a period of 24 weeks, and a consider- 
able variation in the rate of absorption by different 
bricks. 

The application of the test as proposed may serve 
to show whether the absorption is within the proper 
limits for a paving-brick, and when properly applied 
to particular makes of brick may indicate the degree 
of burning, although it may be of much value in the 
comparison of the qualities of different bricks where 
each shows results within reasonable limits. 

SPECIFIC-GRAVITY TEST. 

A test for specific gravity is sometimes included 
in specifications with a view to insuring the burning of 
the brick to the proper density. 

In consequence, however, of the variation of bricks 
made from different materials it does not seem feasible 
to adopt any requirement foi general use which would 



BRICK PAVEMENTS. 199 

be of much value, and as the same qualities are deter- 
mined by other tests it seems unnecessary. The 
Commission of the Brick Manufacturers' Association 
recommend the abandonment of this test. 

COMPARISON OF TESTS. 

When it is desired to compare by tests the relative 
merits of various makes of brick, as in the case of com- 
petitive tests, it becomes necessary to determine the 
comparative values of the results of the different tests 
and give to each a weight in proportion to its impor- 
tance. For this purpose various formulas have been 
proposed in which the results of the separate tests are 
combined into a single term representing the supposed 
value of the brick. Prof. J. B. Johnson proposed the 

T C 

formula V = (25 - R) + (3 - A) + ■ + ■ 

1000 4000 

This has been used to some extent in specifications. 

The formula of the St. Louis Board of Public 

. ... 10 1 r c 

Improvements is V = — H H ■ + - 



Rg \A 2000 4000 
While Mr. H. A. Wheeler proposed the formula 

V = (18 - R) 6 + (7 - A) 4 + — + — • In all 

220 1000 

of these V = value of brick; R = loss in rattler in per- 
centage of weight of brick; T' = the transverse strength 
in terms of load per inch of width; T = modulus of 
rupture per square inch; C = crushing strength per 
square inch. With the range of value commonly 
obtained for paving-brick, Johnson's formula gives a 
weight of 60 or 70 per cent to the rattler test, 10 to 15 
per cent each to the absorption and crushing tests, 
and 8 or 10 per cent to the transverse test; Wheeler's 



200 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

formula gives more weight than Johnson's to the rattler 
test and less in proportion to the transverse test. 
The St. Louis formula gives a weight of about 30 per 
cent to the results of the rattler test and 45 per cent 
to those of the crushing test. 

The rattle test is, without doubt, the most impor- 
tant of these tests, as calling into play more nearly than 
the others the qualities necessary to wear in the pave- 
ment; but in using such a method of comparison the 
conditions which may affect the results of that test 
as already outlined, and the limitations within which 
such tests are properly comparable, should be kept in 
mind. The wisdom of placing such supreme confi- 
dence in the results of this test, and rejecting the use 
of the others even as aids to the judgment, as seems 
to be done by the Commission of the Brick Manu- 
facturers' Association, is at least open to question. 

Specifications for brick pavements commonly require 
that the brick reach certain limiting values on some of 
the tests. The abrasion test is usually employed, the 
ordinary requirement being that the brick shall not 
lose more than 25 per cent of its weight on the standard 
test, although in some cases not more than 20 per cent 
abrasion is allowed. 

The transverse test is commonly employed, requir- 
ing about 1800 to 2000 pounds per square inch as a 
modulus of rupture by the standard test. 

The absorption is frequently limited to from 2 to 
4 per cent where shale bricks are employed, a common 
value being 3 per cent. 

The crushing test and specific-gravity test are some- 
times, although more rarely, used. The main reliance 
is usually placed upon the abrasion and transverse 
tests. 



brick pavements. 201 

Art. 53. Construction of Brick Pavements. 

The work to be performed in laying a brick pave- 
ment, after grading and rolling the road bed (see 
Art. 43), consists in placing the foundation; forming a 
cushion coat of sand over the foundation; laying the 
bricks upon the sand cushion; rolling, or ramming, the 
bricks to a uniform surface and bearing; culling all 
broken and imperfect brick; filling the joints between 
the bricks; cleaning the pavement and opening it to 
traffic. 

Foundation. A brick pavement should have a firm 
foundation. As the surface is made up of small inde- 
pendent blocks, each brick must be adequately sup- 
ported from below, or the loads coming upon it may 
force it downward and cause unevenness. The wear of 
the pavement depends very largely upon the mainten- 
ance of a smooth even surface, as any unevenness will 
cause the bricks to chip on the edges, and also produce 
impact from the loads passing over the pavement. 

The best foundation for a brick pavement is doubt- 
less one of concrete, laid after the manner given in 
Art. 47. For light or moderately heavy traffic, such as 
that of the ordinary small city where the road-bed is 
of firm soil and properly drained, the concrete is usu- 
ally placed 4 to 6 inches thick. If the traffic be very 
heavy 9 inches may be necessary, and where from an3^ 
cause the road-bed is not firm it may be advisable to 
still farther increase the depth. 

Under comparatively light traffic a foundation of 
gravel or broken stone as mentioned in Art. 46 maybe 
used. This foundation should, however, usually be 
employed only where traffic is light and the road-bed 
good. 



202 A TEXT-BOOiC ON ROADS AND PAVEMENTS. 

The double-layer pavement (see Fig. 24) consists of 
a foundation made by placing a layer of sand or gravel 
3 to 5 inches thick upon the road-bed, rolling it 
thoroughly and laying a course of bricks upon it. The 
bricks are laid flat with their greatest dimension length- 
wise of the street, as explained in Art. 49. 

This foundation has been more extensively ^used 
under brick pavements than any other, and has often 
given satisfactory results. It is now largely giving 
place to concrete in the better class of work, and in 
many cases under light traffic its economy is question- 
able, as the layer of gravel would often answer equally 
well without the lower layer of bricks. The best base 
to use for a particular work must usually be largely 
determined by the availability of various materials. 

Sand Cushion. The sand cushion consists usually 
of a layer of sand varying, in the practice of different 
engineers, from \ to 2 \ inches in thickness over the 
surface of the foundation. The most common prac- 
tice is to make the sand cushion \\ or 2 inches thick. 
It should be deep enough to admit of the brick being 
driven to a smooth surface, and to take up any in- 
equalities in the surface of the foundation and differ- 
ences in thickness of brick. When a very thin cushion 
layer is employed it is necessary to secure much 
greater accuracy in forming the surface of the founda- 
tion, and it is much more difficult to uniformly bed 
the bricks than when the usual thickness is used. It 
has also been claimed that the thicker sand-bed has 
a marked tendency to diminish the rumbling of the 
pavement. This, however, is perhaps rather doubtful. 
In forming the sand-bed the sand is spread over the 
foundation a little deeper than the bed is to be left, 
and is then drawn off to a smooth surface by the use 



BRICK PAVEMENTS. 



203 



of a form, cut to the desired shape of the surface, 
which extends across the street, and slides on the 
curbs or on stringers laid lengthwise of the street as 
may be convenient. The making of a good firm bed 
requires that considerable sand shall be pulled off 
from all parts of the bed, and the sand should always 
be two or three inches deep against the front of the 
form when drawing it to cut the bed. In order to 
accomplish this, without failing to cut a perfect sur- 
face through the form leaving the guides and riding 
up on the sand, considerable weight is required on the 
form when drawing it. 

The sand for a cushion should be clean and free 
from pebbles, which prevent the formation of a smooth 
bed, and possibly also cause the breaking of the bricks 
in ramming the surface. 

When the sand cushion is 1} or 2 inches deep, an 
allowance of about half an inch is necessary for settle- 
ment in driving the bricks to surface. 

Laying the Brick. The bricks in a street pavement 
are usually laid on edge in courses across the street, 




Fig. 23. 

each alternate course being begun with a half-brick to 
break joints in the courses. This is illustrated in 



204 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



Fig. 23, which represents a pavement as constructed 
for heavy traffic on concrete foundation. 

In many cases the gutter-bricks are turned with the 
greatest dimension lengthwise of the street, with the 
object of facilitating the flow of surface-water in 
the gutter. The advantage of this is doubtful, as it 
has the effect of breaking the bond of the pavement 
between the gutter-bricks and roadway. This is shown 
in Fig. 24, which represents the construction of a 




^g^g 



s s 



-21 



~Z2 



12: 



iia 



' . ,!. J J 1 Q 



SKjJj .' i^iftiWiiiSS 



u 




S&BSKtfm 



Fig. 24. 



double-layer pavement with brick and gravel base, as 
has been commonly used under light or moderate 
traffic. 

In laying the bricks the men stand on the pavement 
already laid and, beginning at a curb, lay three or four 
courses across the street at once, the bricks being 
wheeled and piled on the edge of the finished work 
by laborers working continually in advance of the men 
laying. Wheeling over the newly laid bricks should 
be done on planks, to prevent driving the bricks out 
of surface. The courses may be kept straight and 
close together by driving back each block of eight or 
ten courses, a straight piece of plank four or five feet 
long being held by a handle on top against the side of 



BRICK PAVEMENTS. 20$ 

the course of bricks and lightly struck with a small 
sledge. 

After the bricks are laid across the street the end 
joints are tightened by forcing back each course with 
an iron bar, and closers are fitted into the end spaces. 
Considerable skill is required in this part of the work 
to quickly and accurately fit the closers without 
wasting the material. 

Surfacing the Pavement. After the surface layer of 
bricks is in position it should be swept clean and 
rammed or rolled to a smooth and uniform surface. A 
five- or six-ton roller may be employed, passing three 
or four times over the surface, or a wooden rammer 
loaded with lead to a weight of 80 or 100 pounds may 
be used by striking upon a plank laid lengthwise of 
the street. The plank should be 10 or 12 feet long by 
about a foot wide and 3 inches thick, and used only so 
long as it retains its form and solidity. 

When the pavement has been brought to a surface 
a careful inspection should be made and all defective 
or broken brick removed and replaced, a pair of brick- 
tongs being used for the purpose, and all low bricks 
or low spots being raised and brought to surface. 
A straight-edge is desirable in determining surface, as 
the appearance is often deceptive to the eye, and a 
slight variation in color of brick is frequently mistaken 
for an irregularity of surface. Sometimes the pavement 
is sprinkled and soft bricks picked out by observing 
whether they hold moisture; this method should be 
used with caution and with full knowledge of the 
material, as sometimes a comparatively slight absorp- 
tion will show quite markedly. 



206 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 54. Filling the Joints. 

There is much difference of opinion amongst munici- 
pal engineers concerning the best material to use in 
filling the joints in a brick pavement. The materials 
commonly employed are sand, Portland-cement grout, 
and asphaltic or coal-tar paving-cement. Certain patent 
fillers of more or less the same character are also some- 
times employed. 

Sand Filler. In using sand as a filler, a thin layer 
of sand is spread over the pavement and raked or 
swept into the joints until they are thoroughly filled. 
In some instances the sand is artificially dried before 
putting it upon the bricks, but ordinarily, in mod- 
erately dry weather, the sand may be spread in a thin 
layer on the bricks and allowed to dry before sweep- 
ing in. After the joints are well filled a light layer 
of sand is placed on top of the pavement and it is 
opened to traffic. The jarring of the traffic will 
cause the sand to settle more or less in the joints for 
a considerable time, and the sand cover should be 
retained for several weeks. The sand used for filling 
should be fine and sharp, free from loam and dirt. It 
must not pack or cake on top of the brick under traffic. 
In many instances sand has been used as a filler with 
satisfactory results and given good service even under 
moderately heavy traffic. It makes a practically 
impervious joint and holds the bricks quite firmly in 
place. It seems desirable in the use of sand filler to 
employ round-edge bricks, as the edges are not held so 
firmly as with a rigid filler, and if sharp are more likely 
to be chipped off, while the round edges aid in thoroughly 
filling the joints with the sand. 

Portland-cement Filler. For filling joints with Port- 



BRICK PAVEMENTS. 20*J 

land cement a grout composed of equal parts of cement 
and sand is commonly employed. This grout is mixed 
in a tight box to a condition such that it will readily 
flow into the joints, and is swept in with brooms until 
the joints are thoroughly filled. The easiest method 
of securing the complete filling of the joint is probably 
that of applying the grout in two parts, mixing the first 
part very wet and filling the joints nearly full. As the 
grout begins to stiffen, the draining out of the water 
causes it to settle somewhat, but thoroughly fills and 
seals the lower part of the joint. The second part may 
then be mixed a little stiffer and the upper part of 
the joint be readily filled flush with the top of the 
bricks. 

In handling the grout it is necessary that it be mixed 
quickly and applied at once without giving it time to 
settle, in order that it may retain its consistency and 
no separation of its materials take place. A pavement 
so filled becomes practically a monolithic mass, as the 
bricks are firmly held together and the joint is filled 
flush with the edges of the bricks with a material which 
soon becomes about as hard as the bricks themselves. 

A serious objection to the cement filler is the 
rumbling usually resulting from filling the pavement 
solidly with cement grout, which is doubtless due to 
the expansion of the mortar in the joints. This 
has been doubted by some, on the ground that the 
rumbling is no worse in hot than in cold weather; 
but the expansion which causes rumbling is probably 
that due to the natural swelling of the cement mortar 
rather than that due to temperature. It is well 
known that Portland-cement mortar when kept in 
a damp condition expands considerably for several 
months after it has set. It is also subject to consid- 



208 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

erable changes in dimension with variations in moist- 
ure, and probably the least effect of expansion, rather 
than the greatest, is to be expected in hot, dry weather. 

The rumbling of the pavement may be largely 
obviated by using expansion- joints along each curb and 
at intervals across the street. These joints are com- 
monly made by putting a wooden strip between the 
courses of brick in laying and afterward removing the 
board and filling the joint with asphaltic or coal-tar 
paving-cement before applying the cement grout to 
the pavement. 

To be efficient these joints should not be less than 
f inch when spaced 50 feet apart. Such joints will 
usually be nearly closed in a few months, the paving- 
pitch being forced out by the expansion. After com- 
pletion, the pavement should stand at least a week 
or ten days before it is opened to traffic, to allow 
sufficient time for the cement to harden. During 
this time it should not be exposed to hot sun or per- 
mitted to dry out too much; commonly a light coating 
of sand is spread over it, or sometimes it is dampened 
by frequent sprinklings. 

Bituminous Filler. Bituminous cement is frequently 
used as a filler for brick pavements. In some instances 
this consists of a coal-tar distillate; in others, of asphalt 
cement similar to that used in the surface of asphalt 
pavements; or a mixture of the two may be employed, 
a small amount of asphalt being added to the tar to 
make it less susceptible to changes of temperature. 

On account of the variation in the materials used, 
the results obtained with bituminous fillers have 
differed widely in different places. The difficulty of 
classifying the materials employed, on account of the 
confusion in names used in designating them, makes it 



BRICK PAVEMENTS. 209 

difficult to determine the relative values of the various 
mixtures which have been used for this purpose. In 
many cases very satisfactory results have been obtained 
with these fillers; in others, the susceptibility to tem- 
perature changes has made them failures, the material 
melting and running out of the joints in hot weather, 
and becoming brittle and chipping out in cold weather. 

The bituminous filler, when well constructed, makes 
a very satisfactory filler. It has the advantage over 
sand of being quite impervious to water, while it is not 
so rigid as the Portland-cement filler and does not give 
the rumbling sound to the pavement. 

When bituminous filler is employed it is melted in 
kettles on the street and poured hot into the joints. 
The paving-cement is applied at a temperature of 
250 to 300 F., and should be applied only when the 
bricks are dry. After the joints are filled a light layer 
of sand is spread over the surface, and serves under the 
traffic to clean the surface from any surplus tar which 
may be smeared over it. 

Specifications for bituminous filler differ widely in 
character, in most cases providing no tests, but depend- 
ing upon the manufacturer to provide a suitable 
material. The Chicago, 1907, specifications call for 
"a paving pitch which is the direct result of the dis- 
tillation of ' straight run ' coal tar and of such quality 
and consistency as shall be approved by the Board of 
Local Improvements." The Newark, N. J., specifica- 
tions require a paving pitch " which shall be composed of 
twenty (20) parts of approved refined asphalt, and three 
parts of oil mixed with one hundred parts of pitch, both 
obtained from a direct distillation of coal tar, and 
ordinarily numbered four (4) at the manufactory. 
The proportions must be obtained by weight. The 



I 

2IO A TEXT-BOOK ON ROADS AND PAVEMENTS. 

contractor must furnish the engineer with an affidavit 
from the manufacturer or refiner stating that the 
materials are the kind specified." 

The specifications used by City Engineer E. A. 
Harper in Kansas City in 1907 require the testing of the 
filler in much the same manner that is employed for 
asphalt street surface. They are as follows: 

"Said asphalt filler shall remain ductile at all tem- 
peratures. It shall be an absolute waterproofing. It 
shall firmly adhere to the brick and yet be pliable 
rather than rigid, thus providing for expansion and 
contraction and traffic conditions. This filler shall be 
heated to a temperature of 350 F. or until it will run 
from a dipper without stringing. It shall then be put 
in a cylindrical pointed can and poured between the 
interstices of the brick until the filler is flush with the 
top of the brick. If necessary the interstices shall be 
gone over a second time. 

"It shall be free from water or decomposition 
products. 

"The various hydrocarbons composing it shall be 
present in homogeneous solution, no oily or granular 
character being present. 

"It must, when tested at 77 F., have a penetration 
of from 3 to 9 millimeters when tested for five seconds 
with a No. 2 needle weighted with 100 grams, accord- 
ing to the nature of the asphalt and the conditions 
under which it is employed. It must not be so sus- 
ceptible to changes of temperature that if at 2> 2 ° F. it 
shows a hardness indicated by I millimeter penetra- 
tion, at 1 1 5 F. it will not be so soft as to give more 
than 35 millimeters penetration, using the above 
method of testing. 

"Twenty grams of it shall not lose more than four 



BRICK PAVEMENTS. 211 

(4) per cent in weight upon being maintained at a 
uniform temperature of 32 5 F. for seven (7) hours in 
a cylindrical vessel two and one-half (2^) inches in 
diameter by two (2) inches high. 

"Twenty (20) grams of it shall not lose more than 
eight and one-half (8J) per cent upon being maintained 
at a uniform temperature of 400 F. for seven (7) hours 
in a cylindrical vessel two and one-half (2^) inches in 
diameter by two (2) inches high. 

" It shall be soluble in chemically pure carbon bi- 
sulphide at air temperature to the extent of at least 
ninety-five (95) per cent. 

" It shall not contain of carbonaceous matter insoluble 
in chemically pure carbon bisulphide, air temperature, 
more than four and one-half (4 J) per cent. 

" It shall be soluble in 87 Baume petroleum naphtha, 
air temperature, to the extent of not less than sixty-five 
(65) per cent and not more than eighty (80) per cent. 

" Its solubility in carbon tetrachloride shall not be 
more than one and one-half (1^) per cent less than its 
solubility in carbon bisulphide — both tests being made 
at air temperature. 

" It shall show of fixed carbon not more than fifteen 
(15) per cent. 

" It shall show a flashing point (New York State 
Closed Oil Tester) of more than 350 F. 

" It shall not contain more than five (5) per cent of 
parafin scale, the Holde method of determining parafin 
scale being used." 

Art. 55. Maintenance of Brick Pavements. 

The maintenance necessary for a brick pavement 
consists in keeping it clean and carefully watching it, 
especially during the first year or two years, to see that 



212 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

no breaks occur due to the use of defective bricks in 
the surface or to insufficient support from the founda- 
tion at any point. When any unevenness from either 
of these causes appears, it should «be at once rectified 
before the pavement becomes irregularly worn in con- 
sequence. 

While, as already stated, the utmost care should 
always be taken to use only material of a uniform 
quality in the surface of the pavement, still under the 
closest inspection some inferior material may be used, 
which will only be shown when wear comes on the 
pavement, and unless then removed at once it will 
cause the evenness of the surface to be impaired about 
it. Irregular support from the foundation will be 
less likely to occur in good construction, but its effect 
will be similar to defective material, the sinking of in- 
dividual bricks producing uneven wear. Weak spots 
in the foundation may sometimes be caused, where con- 
crete foundation is not employed, by surface-water 
which is permitted to pass through the joints, saturat- 
ing the sand or gravel beneath and causing it to move 
under concentrated loads. For this reason the joints 
should be observed during the early wear of the pave- 
ment in order to remedy any case where they may not 
have been properly filled. 

Where a brick pavement has been constructed of 
good material and kept in good surface during the 
early period of use, it may then reasonably be expected 
to wear out without any considerable expense for small 
repairs. The length of time the pavement may be 
expected to wear depends upon the quality of the 
materials and the method of construction. For the 
heavier traffic of many of the smaller cities, and 
streets of moderate traffic in the larger cities, brick has 



BRICK PAVEMENTS. 21 3 

shown an endurance which indicates it to be a satis- 
factory and economical material. 

In contracting for the construction of brick pave- 
ments, many cities require the contractor to guarantee 
the pavement for a term of years, making all necessary 
repairs during the period of guaranty. This is intended 
as an assurance of the quality of the work. A guaranty 
of the pavement for one year may often be of use in 
discovering any serious defects in construction, and 
will not add materially to the cost, but the engineer 
in charge of the work has means of accurately judging 
its quality and, where a long period of maintenance is 
required, it is doubtful whether the gain in quality is 
sufficient to warrant the increase in price necessitated 
by the guaranty. 



CHAPTER VIII. 

BITUMINOUS PAVEMENTS. 
Art. 56. Asphalt. 

Asphalt, or asphalt urn, is a mineral pitch which 
occurs in many localities widely distributed over the 
surface of the earth. It consists, in its natural state, 
of bitumen, with a small percentage of foreign organic 
matter, mixed with more or less mineral earth, and 
varies widely in character according to the nature of 
the bitumen that it contains and the amount and kind 
of mineral matter found mixed with it. It also occurs 
in a solid state as limestone impregnated with bitumen, 
commonly known as rock asphalt. 

1 BITUMEN. 

The bitumen which forms the essential part of 
asphalt consists of a mixture of hydrocarbons of 
various compositions and in varying proportions. It 
is not, therefore, a compound of definite composition, 
and little can be inferred from its ultimate analysis 
as to the character of the material. These hydrocar- 
bons are divided into classes according to certain of 
their physical and chemical properties, and the char- 
acter of a bitumen is judged by determining the per- 
centages of each class of hydrocarbons that it contains. 
This division into classes is purely arbitrary, and the 
details of the methods of analysis must be carefully 

214 



BITUMINOUS PAVEMENTS. 21$ 

specified and made uniform in order that the results 
of tests may be comparable for different bitumens. 

Bitumen is separated from the other constituents 
of the asphalt by its solubility in cold carbon bisul- 
phide, any organic matter not soluble being considered 
foreign and not classed as bitumen. Sometimes chloro- 
form or turpentine is used as a solvent for this purpose, 
giving usually a somewhat higher percentage of bitu- 
men in the material. 

The constituents of bitumen have commonly been 
divided into two classes, the first of which, called 
petrolene, is the oily and cementitious material; the 
other, called asphaltene, is the hard material lacking 
in cementing properties. These were separated by the 
solubility of the petrolene in naphtha. Mr. Clifford 
Richardson* has, however, proposed a more extended 
classification, which gives a better definition of the 
character of the material, and has also outlined in 
detail the methods he uses in their determination. 

Petrolenes. Mr. Richardson limits the term "petro- 
lenes" to those hydrocarbons which are volatilized at 
325 F. in 7 hours. The petrolenes, thus defined, are 
found to but small extent in the asphalts used in paving, 
varying from about I J per cent to 6 per cent of the 
total bitumen. 

Malthenes. The name "malthenes" is applied to bitu- 
mens soluble in naphtha solution (of density 88 Baume) 
on account of their resemblance to the malthas. These 
hydrocarbons comprise usually 60 per cent to 71 per 
cent of the total bitumen in asphalts commonly used 
for pavements. They are the heavy oils which tend 
to give plasticity to the asphalt, and lower its melting 
point. 

* The Modern Asphalt Pavement, New York, 1905. 



2l6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Asphaltenes. Asphaltenes are defined as those hydro- 
carbons not soluble in naphtha solution but soluble in 
cold carbon tetrachloride. These form a hard brittle 
substance, which will not melt without decomposition, 
when heated in the absence of malthenes. The 
bitumens of the asphalts in common use are composed 
almost entirely of the malthenes and asphaltenes, the 
relative proportions between the two determining the 
consistency of the material and its availability for, and 
method of use. 

Carbenes. Hydrocarbons soluble in carbon bisul- 
phide but insoluble in cold carbon tetrachloride are 
classed as carbenes. These bitumens have hardened 
through exposure or other causes to a greater extent 
than the asphaltenes and thus become less soluble in 
the oils. They enter to a very limited extent into the 
materials used for asphalt pavements, but sometimes 
occur in bitumens of similar character and serve to 
distinguish between these classes of materials. 

Saturated Hydrocarbons. The distinction between 
saturated and unsaturated hydrocarbons is drawn by 
observing the action of sulphuric acid upon the hydro- 
carbons soluble in 88 degrees solution of naphtha; the 
saturated hydrocarbons being unacted upon while the 
unsaturated ones are removed from the solution by 
the acid. 

Separation of Bitumens. As already stated, each of 
these classes consists of complicated mixtures of hydro- 
carbons of varying compositions and properties, and 
the line between them is arbitrary and indefinite. The 
tests used, therefore, to separate them must be exactly 
defined and made with precision in order to give 
comparable results, and, while they may be employed 
with confidence to control the use of an asphalt of 



BITUMINOUS PAVEMENTS. 217 

known properties, they cannot be conclusive as to the 
value of an untried material. 

These bitumens being composed of a mixture of a 
number of hydrocarbons of different melting points, 
do not melt at any particular temperature, but gradu- 
ally change in consistency with change of temperature, 
softening and finally flowing as the heat increases. It 
is common to determine arbitrarily certain temper- 
atures which are known as the softening and flowing 
points of the material. The consistency or softness 
of the bitumen is commonly determined by the depth 
of penetration, in millimeters, of a needle at standard 
temperature (usually 78 F.). 

TRINIDAD ASPHALT. 

The most important source of supply of asphalt for 
street pavements in the United States is that of the 
island of Trinidad, W. I. This asphalt is known as 
lake asphalt or land asphalt, according to the source from 
which it is obtained. Lake asphalt is found in a large 
deposit known as the pitch lake. This lake covers an 
area of over 100 acres, and lies in a deep crater with 
steeply sloping sides. The pitch seems to be, or to 
have been, forced up from below, and it is more or 
less in motion, excavations in the surface being gradu- 
ally filled by flow of material from sides and bottom. 
Upon exposure to the air, the pitch slowly hardens, 
is somewhat softer near the center of the lake than at 
the sides, and it has been supposed that the supply 
from subterranean sources still continues to some 
extent. It has also been found that the surface of the 
lake is higher in the center than at the sides, and that 
the general elevation of the surface has been lowered 



2lS A TEXT-BOOK ON ROADS AND PAVEMENTS. 

somewhat by the large quantities of material which 
have been removed from it. 

Refined Trinidad Lake Asphalt consists ordinarily of 
about 54 per cent to 57 per cent bitumen, 5 per cent to 
8 per cent of organic matter not soluble in carbon 
bisulphide, and 35 per cent to 38 per cent of mineral 
matter. The bitumens contain about 63 per cent to 
66 per cent of malthenes (according to Richardson's 
classification), the remainder being asphaltenes, with 
sometimes about 1 per cent of carbenes. These asphal- 
tenes contain considerable sulphur and are hard, 
brittle substances, which do not melt but are readily 
soluble in the asphaltic oils. The non-bituminous 
organic matter is mainly material which seems to have 
been formed through oxidation of some of the harder 
bitumens of the asphalt. It contains a considerable 
amount of sulphur and may be considered, like the 
finely divided mineral matter, -as of use as filler. The 
mineral matter in Trinidad asphalt is found in a finely 
pulverized condition and quite uniformly distributed 
through the mass. 

The so-called land asphalt from Trinidad is found in 
vicinity of the lake, and is a harder material than lake 
asphalt, probably from longer exposure to the air. 
It may have been derived either from the overflow of 
the lake or from independent subterranean sources, the 
action in which has long ceased.* 

Refined Trinidad Land Asphalt consists commonly of 
about 51 per cent to 55 per cent bitumen, 7 per cent 
to 10 per cent, organic matter insoluble in carbon 
bisulphide, and ^J per cent to 40 per cent of mineral 

* For a complete description of the Trinidad pitch deposits see the 
"Report of the Inspector of Asphalts and Cements of the District of 
Columbia," for 1891-92. 



BITUMINOUS PAVEMENTS. 219 

matter. The bitumen contains from 50 per cent to 63 
per cent of malthenes, soluble in 88° naphtha solution. 
The character of the land asphalt is more variable 
than that of the lake, and seems to depend upon the 
length of time it has been exposed to the weather. 
The bitumen of the asphalt undergoes a gradual harden- 
ing with time, the percentage of malthenes becoming 
less as compared with that of the asphaltenes. In some 
instances the amount of mineral matter is greater, 
while the non-bituminous organic matter is increased by 
the changing of some of the bitumen to an insoluble 
condition. 

BERMUDEZ ASPHALT. 

The asphalt obtained from the State of Bermudez, 
Venezuela, is derived from what is known as the Ber- 
mudez "Pitch Lake." This deposit is much greater 
in area than that at Trinidad, being some 800 acres in 
extent. It is, however, shallow in depth; not, as in 
Trinidad, in a deep crater, but spread out in a flat 
layer over the surface of the ground from a number of 
springs, some of which are still active. The asphalt 
has come from the spring in a soft condition and 
afterward hardened by exposure, a crust forming on 
top which is cut through in getting the asphalt from 
beneath. The asphalt from Bermudez is nearly pure 
bitumen, containing very little mineral matter, but the 
bitumen is more variable in character than that from 
Trinidad. 

Refined Bermudez Asphalt contains usually 93 per 
cent to 97 per cent bitumen, 2 per cent to 5 per cent of 
other organic matter, and I per cent to 3 per cent in- 
organic, or mineral matter. The bitumen contains 
64 per cent to 72 per cent of malthenes soluble in 88 



220 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

degrees naphtha solution, and has 2 per cent to 5 per 
cent of petrolenes, volatile at 325 F. in 7 hours. It is 
therefore somewhat softer and more volatile than the 
Trinidad asphalt. 

Another deposit of asphalt in Venezuela produces 
material known as "Maricaibo asphalt" somewhat 
similar to the Bermudez asphalt and used for paving. 

CALIFORNIA ASPHALT. 

Several deposits of asphalt in Southern California 
have been developed and more or less used for paving 
purposes. The individual deposits in most cases are 
small in extent and somewhat expensive to work. The 
asphalt usually differs from those already described in 
being harder, the bitumen containing less malthenes. 
Some of them have a higher percentage of mineral 
matter and less bitumen than the Trinidad; others 
have only a small amount of mineral matter but are 
composed of a harder bitumen. 

Bitumen similar to that in the natural asphalts is 
produced as a residual pitch in the distillation of the 
asphaltic petroleums of California. The character of 
this bitumen depends upon the extent to which the 
distillation is carried and the care used in the opera- 
tion. With proper manipulation of the process the 
product may be controlled and the proportions of 
malthenes and asphaltenes regulated. Where the 
material is overheated and burned, some of the asphal- 
tenes are changed to carbenes, or to insoluble organic 
matter. 

UTAH ASPHALT. 

Considerable deposits of asphaltic materials are found 
in Utah and Colorado. Of these, the most important 



BITUMINOUS PAVEMENTS. 221 

are large deposits of nearly pure bitumen known as 
Gilsonite. This material differs from the bitumen of 
Trinidad and Bermudez asphalts in the small percen- 
tage of saturated hydrocarbons which it contains. 
The Utah gilsonite is used to considerable extent for 
paving and also in the preparation of asphalt cement 
for filling the joints in brick and stone pavements, as 
well as asphalt paints and waterproofing mixtures. 

ASPHALTIC SAND. 

Deposits of sand impregnated with asphalt occur at a 
number of points in California, Kentucky, Utah, and 
Indian Territory. These deposits consist of sand, or 
sandstone, saturated with bitumen. They differ from 
each other in the amount of bitumen found in them, 
and in the sand grains. They contain from about 5 
per cent to 20 per cent of bitumen, which in most 
instances have a larger percentage of malthenes and 
are much softer than those of the Trinidad and Ber- 
mudez asphalts. They also frequently contain con- 
siderable petrolene, or matter volatile at 325 F. in 
7 hours; in some instances as much as 10 per cent to 
12 per cent. These materials have been used to some 
extent in paving. In California the bitumen has been 
extracted from the sand by the use of maltha and then 
refined and used in the same way as the Venezuela 
asphalts. The Kentucky asphaltic sandstones have 
been used by adding to them a harder bitumen, and 
finer mineral matter for filler. The Indian Territory 
material has been used for pavements by mixing it 
with an asphaltic limestone which also occurs in the 
same locality. 



222 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

ROCK ASPHALT. 

Limestone impregnated with bitumen occurs in 
many places in Europe and a few localities in the 
United States. The rock is mined at a number of 
places in Europe, notably at Seyssel, France; Travers, 
Switzerland; Ragusa, Italy; and Verwohle, Germany. 
It is usually composed of nearly pure carbonate of 
lime, impregnated with from 5 per cent to 20 per cent 
of bitumen. Natural rock asphalt suitable for paving 
purposes usually contains from 9 per cent to 20 per 
cent of bitumen. The rock should be of fine, even 
grain, and have the bitumen uniformly distributed 
through it. In forming the surface material for pave- 
ments, the rock from different mines is commonly 
mixed in such proportions as to give about 10 per cent 
to 12 per cent of bitumen in the mixture. 

Deposits of bituminous limestone exist in Texas, 
Indian Territory, and Utah in the United States. 
That of the Indian Territory has, as already stated, 
been used for paving in connection with asphaltic 
sand. 

ASPHALTIC CEMENT. 

Crude asphalts as they occur in nature usually con- 
tain considerable water, which needs to be removed 
before the material can be used. In order to remove 
this water and any vegetable impurities which the 
crude material may contain, the asphalt is refined by 
heating sufficiently to vaporize the water and melt 
the bitumen. This is accomplished either by the use 
of a large kettle heated directly by fire, or by passing 
steam through pipes inside the tank containing the 
asphalt. During the heating the material is agitated 



BITUMINOUS PAVEMENTS. 223 

by a current of air or steam. When the water has been 
driven off, and the material is thoroughly melted, 
the liquid asphalt is drawn off and is known as refined 
asphalt. Some asphalts occur in a practically anhy- 
drous condition and do not need refining. 

Refined asphalt is brittle at ordinary temperatures 
and possesses little cementitious value. To bring it 
to a proper consistency it is heated to a temperature 
of about 300 F. and mixed with heavy bituminous 
oil, which serves as flux. The product is then known 
as asphalt cement: 

Fluxes. The material commonly used to soften 
asphalt in preparing paving cement is the oil residuum 
resulting from the distillation of petroleum. In the 
distillation of the petroleum the lighter oils are driven 
off, the petrolenes being removed. The material re- 
maining is composed of bitumens similar in character 
to those of the asphalts, and when carefully prepared, 
almost entirely malthenes (soluble in 88° naphtha 
solution). These residuums differ considerably in 
character according to the nature of the petroleum 
from which they are prepared and the care used in the 
preparation. Those prepared from the California 
asphaltic petroleums differ from the residuums of 
Eastern petroleums in containing less saturated hydro- 
carbons, and in having no parafnnes, the presence 
of which characterize most of the other residuum 
oils. 

Natural malthas have sometimes been used as fluxes 
for asphaltic cement, but in most instances difficulty 
has been met in their use due to the fact that 
they contain considerable of the lighter oils, petrolenes, 
which are volatilized at the temperature required for 
mixing, thus leaving the maltha too hard to act 



224 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

satisfactorily as a flux. The same difficulty is met in 
use of carelessly prepared petroleum residuum, which 
may lack uniformity of composition, and contain both 
volatile oils and hard asphalt enes. 

The amount of fluxing materials necessary to give 
proper consistency to asphalt cement depends upon 
the density of the oil as well as the nature of the asphalt. 
With dense and heavy oils a larger amount of oil 
must be used to reach the same consistency than with 
light oils, and the stability of the mixture is greater 
when maintained in heated condition for a long time, 
on account of the less volatile nature of the oils. For 
Trinidad and Bermudez asphalts the amount of resid- 
uum oil required may vary from about 15 per cent 
-to 25 per cent of the weight of the asphalt. For 
harder asphalts a larger quantity is required, and 
where the amount of malthenes in the bitumens is 
low, a high percentage of dense oil may be required 
in order to give a proper relation between the mal- 
thenes and asphaltenes in the resulting asphaltic 
cement. 

Preparation of Cement. In preparing asphalt cement 
the asphalt is first melted and raised to a temperature 
of about 300 F. The flux is then added at a tempera- 
ture of 150 to 200 F. The mass is then agitated 
with jets of steam or air. The agitation is continued 
from 4 to 8 hours, or until the mass comes to a uni- 
form and homogeneous condition. The refined asphalt 
cement is then drawn off. 

Careful and expert manipulation is necessary to 
secure a uniform product of proper consistency. 
Continued agitation with air causes hardening of some 
of the bitumens and volatilizes some of the lighter 
oils. The consistency is commonly tested by chewing 



BITUMINOUS PAVEMENTS. 225 

in the mouth a small piece of the asphalt cement 
which has been cooled in water. For accurate deter- 
minations, the penetration is determined, at standard 
temperature, by a penetration machine (see Art. 58). 

Art. 57. Surface Mixtures. 

The material commonly employed for the surfaces 
of asphalt pavements consists of a mixture of asphalt 
cement, powdered limestone, and sand. The mixtures 
used in different places have varied considerably in 
character, according to the nature of the materials 
available and the amount and consistency of the 
bitumen employed. Experience has gradually devel- 
oped the practice in different places, the work at first 
being largely experimental, defects in the early work 
being corrected by modifications in later mixtures. 
Much of this work has been done by very haphazard 
methods and without any careful analysis of the 
causes of defects and failures, or of the differences in 
materials used in different places. 

Sand. It is common to grade sand in size by 
sifting through sieves of 10, 20, 30, 40, 50, 80, 100 and 
200 meshes to the linear inch, finding the percentage 
which passes each sieve and is caught by the next 
finer one. The portion which passes the 200-mesh 
sieve is too fine to be considered as sand, and is classed 
with the stone powder which is added as filler. The 
sands used for asphalt surface mixtures are much 
finer than those employed in cement mortars. In 
sand for this purpose most of the sand is usually fine 
enough to pass the 40-mesh sieve. In some instances, 
the bulk of the sand will pass through the 80 and 1 00- 
mesh sieves; in others, the larger portion will only pass 



226 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the 40 and 50-mesh sieves. A grading of sizes in the 
sand is desirable on account of reducing the amount 
of voids to be filled by the asphalt, and frequently 
when a natural sand of correct sizes is not available, 
it is possible to secure a proper relation of sizes of 
grain by mixing two or more sands of differing sizes. 
In general, sand so graduated as to leave a small 
percentage of voids is desirable in order that the 
interstices may be fully filled with bitumen, but the 
sand of greatest density is not necessarily the best 
for this purpose, as there may be instances where the 
percentage of voids would not admit of a sufficient 
amount of bitumen. 

The voids in the sand are commonly tested by 
filling a measure with packed sand and then deter- 
mining the quantity of water that can be added to it. 
A better method with fine material is to determine 
the specific gravity of the sand and also the weight of 
a given volume of it, the volume of voids being the 
difference between the measured volume and the 
volume of solid matter represented by its weight. 

The sand used should be hard and tough in order to 
resist wear well, but its chemical character is not of 
special importance, although there seems to be a 
difference in the adherence of bitumen to the surfaces 
of different sands. The reason for this difference is 
not apparent and cannot be judged in advance of actual 
trial. The shape of grain does not usually appear 
important. Rounded grains often pack more easily 
and form a more dense mass, but it has been sometimes 
thought that they move more readily upon each other 
and form a less firm surface. 

Filler. The filler used in asphalt paving mixtures 
consists of very finely ground mineral matter mixed 



BITUMINOUS PAVEMENTS. 227 

with the bitumen for the purpose of rendering the 
surface more dense, and giving stiffness to it. The 
material commonly used for this purpose is ground 
limestone, although a number of other materials have 
been employed. Ground clay may make a good 
filler; slaked lime, and Portland or natural cement 
are also used, especially good results being obtained 
with Portland cement. 

The filler should be finely ground; nearly all of it is 
usually required to pass a 200-mesh sieve, but the 
finer portions are too fine to be graded by the use of 
sieves. For this purpose the method of elutriation 
may be employed. By this method the powders of 
different degrees of pulverization are separated by 
observing the times required to settle after being shaken 
in a vessel of distilled water, the portions which settle 
in 15 seconds, one minute, and 30 minutes being deter- 
mined, and the relative fineness of different samples 
thus compared. 

Composition of Mixture. The relative amounts of 
asphalt cement filler, and sand required for a surface 
mixture must of course depend upon the properties of 
these materials. The fineness of the sand and of the 
filler, and the amount of mineral matter in the cement, 
are all important in determining the proper propor- 
tions. The proportions of materials are determined 
by weight, the purpose being to secure a proper 
amount of bitumen and of dust, as compared with 
the sand in the resulting mixture. The amount of 
bitumen required varies from about 9 per cent to 13 
per cent, most commonly between 10 per cent and 1 1 
per cent. Mr. Richardson gives* the following mixture 

* The Modern Asphalt Pavement, N. Y., 1905. 



228 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



as a standard to be used for surfaces of Trinidad 
asphalt pavements: 



Bitumen 

Passing — 

200-mesh sieve 
ioo-mesh sieve 
8o-mesh sieve 
50-mesh sieve 
40-mesh sieve 
30-mesh sieve 
20-mesh sieve 
10-mesh sieve 



Surface Mixture. 


Sand. 




Per cent. 


Per cent. 




10 -5 

13.0 
13.0 








17 .0 




13 .0 


17 .0 




23 -5 


30.O 




11 .0 


13.0 




8.0 


10 .0 




5-o 


8.0 




3-° 


s-° 




100 .0 


IOO .0 





This he regards as an exceptionally good mixture. 
As the sands used in practice vary in the proportion 
of fine grain which they contain, the amount of 
bitumen must be correspondingly varied. When a 
larger portion of the sand passes the 80 and ioo-mesh 
sieves, a larger amount of bitumen and of filler may be 
introduced. When the sand is coarser, a smaller 
amount of bitumen is necessary in order that the 
pavement may not be soft enough to mark under the 
horses' feet. In sand which lacks the finer grains 
the percentage of bitumen which can be used without 
marking is often so low as to leave the material too 
porous and liable to the action of water. It is desir- 
able that the mixture contain all the bitumen that it 
will carry by the addition of filler without becoming 
too soft. A lack of bitumen may cause cracking of 
the surface. The quantity of bitumen required is 
also somewhat affected by the character of the sand 
grains and the extent to which the bitumen may adhere 



BITUMINOUS PAVEMENTS. 229 

to and coat the grains. Some sands will "take' 
more bitumen than others of the same grading of sizes 
without leaving a surplus of bitumen to render the 
material too soft. 

The amount of bitumen to be used in a surface mix- 
ture is commonly tested by the pat test. This consists 
in pressing a pat of the surface material in a piece of 
brown manila paper and observing the stain left upon 
the paper; the depth of the stain indicates to the 
experienced eye whether the right amount of bitumen 
has been used and whether the mixture has been prop- 
erly prepared. An impact test is also sometimes made 
to determine the resistance of the surface material to 
marking, and frequent analyses are made to test the 
correctness of the mixture. 

The traffic to which a street is subjected has much 
to do with the consistency required in the surface 
mixture. For streets of light traffic a softer mixture 
should be employed than for one with heavy traffic. 
The rolling out and working of the surface by heavy 
traffic will admit of a hard surface material which might 
crack under light traffic. The surface mixtures must 
in every case be suited to the local conditions of traffic 
and weather, that it may neither mark under the 
impact of traffic nor crack from shrinkage in cold 
weather. 

Method of Mixing. In the preparation of the surface 
mixture, the sand and asphalt cement are heated 
separately and then mixed while hot. When two or 
more sands are used to obtain the proper grading of 
sizes, this mixing must first be accomplished, and great 
care is necessary in handling the sand in mixer and 
heater to prevent the segregation of sizes and bring the 
sand in uniform mixture at proper temperature (about 



230 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

330 to 350 F.) to the final mixture. The asphalt 
cement is also heated in a large heater where it is 
agitated by steam jets to maintain the uniformity of 
mixture. 

The surface mixture is prepared in a mixer of small 
size which mixes 10 to 15 cubic feet at one operation, 
and is so arranged as to load directly into the wagon 
which takes it to the street. The mixing is accom- 
plished by blades revolving on shafts in the mixing 
tanks, requiring about one to two minutes to make a 
complete mixture. The proportioning of the ingredi- 
ents is accomplished by weighing the proper quantity 
of each of the materials for a batch; the sand and filler 
are first introduced and mixed dry, and the asphalt 
cement then added and the whole mixed together. 
The mixture is then carried to the street at a tempera- 
ture above 300 F. 

Rock Asphalt. The preparation of surface material 
with rock asphalt consists only in crushing and grinding 
the rock to powder, and heating the powder to drive 
off the water and soften the bitumen, so that it may 
be compacted in the pavement. The powder is heated 
to a temperature of 200° to 300 F. and is applied hot 
in laying the surface. 

In determining a mixture of asphalt rock, as in the 
case of other asphalts, the local conditions of climate 
and traffic must be considered and the quantity of 
bitumen be so proportioned as to remain solid in sum- 
mer and not to become brittle and lose cohesion in 
winter. Experience with the material and exercise of 
great care in the determination of proper proportions 
are therefore essential to success in the construction 
of any asphalt pavement. 






BITUMINOUS PAVEMENTS. 23 1 

Art. 58. Tests for Asphalt Cement. 

For the purpose of controlling the character of 
the surface mixtures to be used upon asphalt pave- 
ments, tests are commonly made of the asphalt 
cement, as well as of the surface mixture itself. In 
testing asphalt cement the total amount of bitumen 
is usually determined; the hydrocarbons composing 
the bitumen are separated into their various classes, 
and the consistency of the mixture as well as the effect 
of temperature upon the consistency is examined. 

Total Bitumen. The total bitumen in asphalt, or 
asphalt cement, is determined by testing its solubility 
in carbon disulphide. The following method is recom- 
mended as standard by the "Committee on Standard 
Test for Road Materials/' of the American Society for 
Testing Materials.* 

" It was decided, owing to the great variety of con- 
ditions met in asphalt and like bitumen, that it was 
impossible to specify any one method of drying that 
could be at all satisfactorily applied in every case; it 
is therefore supposed that the material for analysis has 
been previously dried either in the laboratory or in 
the process of refining or manufacture, and that mois- 
ture if preserved, is only hydroscopic or in such a con- 
dition as to be easily removed. 

"The material to be analyzed, if sufficiently hard and 
brittle, is ground and then spread in a thin layer in 
a suitable dish (iron or nickel will do), and kept at a 
temperature of 125 C. for one hour. In the case of 
paving mixture, where it is not desirable to crush the 
sand grains, a lump may be placed in the drying oven 
until it is thoroughly heated through, when it can be 

* Proceedings, American Society for Testing Materials, Vol. VI, 1906. 



232 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

crumbled down with a spatula. From 2 to 12 grams 
(depending on its richness in bitumen) of the substance 
after drying is weighed in a large-sized test-tube (8 
inches long by I inch in diameter), the tare of which 
has been previously ascertained. The tube is then 
tightly corked with a good sound cork and shaken 
vigorously until no asphalt can be seen adhering to the 
bottom or sides, or if a paving mixture or like material, 
until the solvent has disintegrated all lumps. Care 
must be taken that the bottom of the cork should be 
free from any cracks or holes that might retain insoluble 
matter from the asphalt, or if not, the end of the cork 
inserted in the tube must be covered with tin foil. 
Care should be taken while shaking, to keep one finger 
on the cork to prevent it being blown out. 

"The tube should then be put away, still corked 
loosely, in an upright position and not disturbed for 
two days, after which the carbon disulphide is decanted 
off into a second tared tube. As much of the solvent 
should be poured off as is possible without losing any 
of the residue. The first tube is again filled with fresh 
carbon disulphide and shaken as before and put away 
for two more days. The second tube is also corked 
and put away in an upright position. At the end of 
the two days the contents of these two tubes are 
decanted off on to a weighted Gooch crucible fitted 
with an asbestos plug filter, the contents of the second 
tube being passed through the filter first. The asbestos 
filter shall be made of ignited long fiber amphibole, 
packed in the bottom of a Gooch porcelain crucible to 
a depth of about one-eighth of an inch. The residue 
in the second tube is then treated with about 2 cubic 
centimeters of carbon disulphide, care being exercised 
to disturb it as little as possible, the treatment merely 



BITUMINOUS PAVEMENTS. 233 

being to remove the small portion of solvent containing 
bitumen. The Gooch crucible is then washed with 
clean carbon disulphide until the filtrate is colorless. 
The crucible and the two tubes are then dried at 
225 F. and weighed. The nitrate containing the 
bitumen is evaporated and the bituminous residue 
burnt, and the weight of the ash added to that left in 
the two tubes and Gooch crucible. The sum of these 
weights deducted from the weight of the substance 
taken gives the weight of the bitumen extracted/' 

Bitumen Soluble in Naphtha. This test is employed 
for the purpose of determining the relative amounts of 
asphaltenes and malthenes present in the bitumen. 
When used in specifications it is designed to insure a 
proper relation between these classes of hydrocar- 
bons, the object being to avoid materials containing 
too great percentage of asphaltenes, and the use of 
light oils as fluxes. The Committee of the American 
Society for Testing Materials recommend that the 
same method be employed as for obtaining the total 
bitumen. They also recommend that the naphtha 
used be described by giving the temperatures between 
which it distills and its specific gravity. Naphtha of a 
density of 88° Baume at 6o° F. is commonly employed 
for this purpose. 

Heat Test. This test is employed to determine the 
amount of the lighter and more volatile hydrocarbons 
in the bitumen. It separates the petrolenes from the 
heavier hydrocarbons (malthenes and asphaltenes). 
The test is made by determining the loss in weight 
suffered by the material upon being heated for a 
definite time at a constant temperature. It is designed 
to show whether the asphalt cement will be materially 
changed by heat in forming the surface mixture. In 



234 A TEXT-BOOK ON. ROADS AND PAVEMENTS. 

making the test, cylindrical dishes about 2\ inches in 
diameter and I to 2 inches high are commonly em- 
ployed. Mr. Richardson * recommends the use of 20 
grams of the asphalt cement, heated to a temperature 
of 325 F. or 400 F. for 7 hours. For this purpose it 
is necessary to have an oven which can be maintained at 
a uniform temperature. Mr. Dow has suggested! that 
the temperature to be used in the test should be varied 
according to the heat required in working the material. 

" It is to be hoped in the near future that an improved 
modification of this test can be adopted on the following 
lines: As there is considerable variation in the degree 
of temperature at which different asphaltic cements 
become sufficiently liquid to mix with the mineral 
ingredients, this test would be more practical if the 
cements were tested at the temperatures at which it is 
practical to work them. As for example: one cement 
may be so fluid at 250 as to be capable of mixing just 
as well as another one at 300 . In the testing of these 
two cements it would only be necessary to test the one 
at 250 and the other at 300 . This modification in 
the test will be adopted as soon as an apparatus has 
been perfected for determining the viscosity of molten 
asphalt cements at high temperatures/' 

Penetration Test. The consistency of asphalt cement 
is determined by measuring the penetration of a No. 2 
needle under a standard weight (usually 100 grams), 
in a given interval of time (commonly 5 seconds) . The 
tests must be made at a standard temperature (usually 
77 F.). Machines for making this test have been 
devised by Mr. A. W. Dowf and by Clifford Richardson. J 

* The Modern Asphalt Pavement, New York, 1905. 

f Proceedings, American Society for Testing Materials, Vol. III. 

% Proceedings, American Society for Testing Materials, Vol. VII. 



BITUMINOUS PAVEMENTS. 235 

The Dow apparatus consists of a No. 2 needle in- 
serted in a short brass rod which is held in an aluminum 
rod by a binding screw. The aluminum rod is secured 
in a framework so balanced that when it is supported on 
the point of the needle the framework and rod will 
stand in an upright position, allowing the needle to 
penetrate perpendicularly without the aid of support. 
The frame, aluminum rod, and needle weigh 50 grams; 
additional iweight, when desired, is placed on the bot- 
tom of the frame. The motion of the sliding part is 
communicated by a thread to an index arm moving 
over a graduated disk. 

"To make the penetration test, the samples of 
asphalt cement contained in circular tins, along with 
the glass dish, are placed in a receptacle containing 
at least 5 inches of water, which should have been pre- 
viously brought to the temperature at which it is 
desired to make the test. While the samples are under 
the water it should be stirred every few minutes, best 
with a thermometer, and the temperature kept con- 
stant when necessary by the addition of hot or cold 
water as the case may require. The samples should 
remain under water at least 15 minutes, and in cases 
where their temperature is not near that at which 
the test is made they should be left in possibly half an 
hour. After the samples have remained in the water 
a sufficient time to have attained its temperature they 
are ready to be penetrated." 

For the purpose of determining the effect upon con- 
sistency of changes of temperature, tests are made of 
the penetration at different temperatures. Mr. Dow 
recommends the following standards: "The needle 
which I have adopted as a standard for penetration 
is a No. 2, manufactured by R. J. Roberts, Redditch, 



236 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

England. All the needles, however, obtained in a 
package cannot be used for penetrating, as they vary- 
somewhat in shape, and only those are selected which 
give a penetration corresponding to the standard 
needle. The standards that I have adopted for this 
machine are : At 32 F. or lower, the distance in one- 
hundredths of a centimeter that a No. 2 needle will 
penetrate into the sample in one minute of time when 
weighted with 200 grams. For tests made at a tem- 
perature of 77 F., the distance in one-hundredths of 
a centimeter that a No. 2 needle will penetrate into 
the sample in 5 seconds of time when weighted with 
100 grams. For tests made at a temperature of 100° F., 
or above, the distance in one-hundredths of a centi- 
meter that a No. 2 needle will penetrate in 5 seconds of 
time weighted with 50 grams. 

" The following is a table giving the penetration and 
ductility of three classes of asphalt cement, which I 
have designated as A, B, and C : 



A 


B 


10 


13 


55 


47 


150 


no 


35o 


220 


300 


75 



Penetration at — 

32 F 10 13 25 

77° F 55 47 45 

100 F 150 no 75 

115 F 110 220 120 

Ductility at 77 F 



" It has been found from practical experience that 
it is not safe to use an asphalt that is more susceptible 
to changes in temperature than sample A, given in 
the table, for if it were more susceptible than this, 
and made to a softness to give sufficient ductility at 
low temperatures, it would be too soft for use at high 



BITUMINOUS PAVEMENTS. 23/ 

temperatures. The average paving cement gives 
penetrations such as represented by B in the table. 
Sample C in the table represents the least susceptible 
cement which I have found on the market. This non- 
susceptibility to change in temperature would be of 
great advantage if it were not for the fact that the 
cement is lacking in ductility. There is a law which 
I have found that invariably applies to the proper- 
ties of asphalt cements, that is, that the less susceptible 
cement is to change in temperature, the less ductile it 
is at normal temperatures, and inversely, the more 
susceptible the more ductile is the cement/' 

Test for Ductility. Mr. A. W. Dow * has proposed 
a test of the ductility of asphalt cement by determining 
the distance in centimeters that a prism of cement can 
be drawn out before breaking. The prism he uses is 
5 centimeters in length with a square cross-section of 
I centimeter. The test piece is molded with the ends 
in clips, which may be attached to apparatus for 
applying the pull. The clips are pulled apart at a 
speed of I centimeter per minute, while immersed in 
water at the required temperature. " Sufficient work 
has not been done on the ductility test at low temper- 
atures to be able to state any standard at the present 
time, but it has been found that it is not safe for an 
asphalt having a consistency of 40 penetration at 77 F. 
to pull less than 20 centimeters at this temperature in 
the above ductility test/' 

Impact Test. An impact test for the purpose of 
determining the toughness of asphalt surface mixtures 
has been proposed by Messrs. Richardson and Forrest. f 
"The test pieces were made as follows: The surface 

* Proceedings, American Society for Testing Materials, Vol. III. 
f Proceedings, American Society for Testing Materials, Vol. V. 



238 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

mixture was brought to such a temperature as would 
be found necessary in handling it upon the street, a 
weighed amount, such as has been found by experi- 
ence would yield a cylinder after compression of I 
inch in height, is placed in a cylindrical mold, closely 
resembling the ordinary diamond mortar of the labo- 
ratory, of a diameter of 1} inch. The mold is supported 
on the rigid block of timber I if by 9 J inches square 
by S 2 i inches high. The warm steel plunger is placed 
upon the top of the hot mixture, above which is a 
cylinder of steel weighing 10 pounds, running in 
grooved guides, which can be allowed to fall upon it 
from a height of 3 feet. After a few gentle taps to seat 
the plunger, the weight is raised and allowed to fall 
freely 10 times. The cylindrical mold is then inverted 
and the plunger introduced at the other end in a space 
left for this purpose by a boss on the base supporting 
the mold. Ten additional blows are then given on 
this end of the cylinder. In this way it has been found 
that satisfactory and uniform compression is obtained. 
The cylinders are then weighted to determine if the 
density is satisfactory, and measured to see that they 
are of uniform height, I inch or nearly so. On cooling 
they are ready to be tested, in the same manner 
employed by Mr. Page for rock cylinders, at whatever 
temperature may be selected" (see Art. 37). 

Separation of Bitumen. For the purpose of testing 
the bitumen in surface mixtures, or in asphalt cement 
containing considerable mineral matter, it may be 
necessary to separate the bitumen from the mixture. 
The following method is given by Mr. Dow: * "The 
pure bitumen is obtained from an asphalt, or asphaltic 
cement, by extracting with carbon disulphide and 

* Proceedings, American Society for Testing Materials, Vol. III. 



BITUMINOUS PAVEMENTS. 239 

evaporating off the solvent. The procedure that I 
have found to give the best results is as follows : Suffi- 
cient of the asphalt or asphaltic cement to give 30 
grams of pure bitumen is placed in a large Erlenmeyer 
flask. Between 300 and 400 centimeters of carbon 
disulphide is added, the flask corked and then shaken 
from time to time until none of the asphalt is seen 
adhering to the sides or bottom, after which the flask 
is set aside and allowed to stand for 24 hours. The 
carbon disulphide is then decanted off carefully from 
the residue into a second flask. The residue is again 
treated with 200 or 300 cubic centimeters of the 
solvent and shaken as before. After the solutions 
in the two flasks have been allowed to subside for 24 
hours, the contents are carefully decanted off on to an 
asbestos filter, passing the contents of the second 
flask through the filter first. The solvent containing 
the bitumen is then distilled in a flask until just suffi- 
cient remains to have the contents liquid. It is then 
poured into a flat evaporating dish and further heated 
on the steam-bath, stirring from time to time, until 
the greater part of the carbon disulphide is evaporated. 
About one-half cubic centimeter of water is next 
incorporated into the residue of bitumen and the heat- 
ing continued over a burner until all foaming ceases, 
after which it is kept at 300 F. for 10 minutes. 
While heating over the burner the bitumen should be 
stirred constantly with a thermometer and care exer- 
cised that the temperature is kept constant at 300 F. 
It is doubtful whether in all cases the last traces of 
carbon disulphide are removed, even by this method, 
and it is also likely that the bitumen obtained in this 
way is often slightly harder than that contained in 
the original asphalt or cement; but its physical prop- 



240 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

erties, as far as ductility and susceptibility to change 
in temperature go, will be relatively the same, and a 
sufficiently close approximation can be made of the 
consistency of the bitumen in the original sample to 
answer all practical purposes. As the removal of the 
last traces of carbon disulphide is very difficult, and a 
soft bitumen is liable to be hardened in so doing, I 
make it a practice, wherever it is possible, to extract 
the bitumen from an asphalt before it has been soft- 
ened into the paving cement. In this way I find it 
easier to remove the last traces of solvent from this 
hard bitumen, and at the same time with relatively 
less hardening. This bitumen from the asphalt is 
then fluxed into a paving cement by adding to it an 
amount of flux equivalent to that used in making the 
paving cement from the asphalt. It is fortunate that 
nearly all the asphalts met with in commerce that are 
not pure bitumen are of a hard nature, so that the 
above method is applicable in practically all cases. 
This of course does not apply to bituminous rock, and 
the only way possible to estimate their quality is by 
examining the extracted bitumen, which is done as 
just described. It is well to note here that in cases 
where the bitumen hardens materially in the removal 
of the solvent, such a bitumen will be rejected by 
hardening too much in the heat test." 

Tests Required by Specifications. Many tests have 
been proposed for the control of asphalt paving mix- 
tures, or used in the study of asphalt materials, by 
various investigators. In general, however, specifi- 
cations used by municipal engineers have depended 
upon a contractor's guaranty for the character of the 
work rather than upon inspection of the materials and 
workmanship. This has not proven altogether satis- 



BITUMINOUS PAVEMENTS. 24 1 

factory in many places, and some cities employ expert 
inspectors and depend upon their own tests for the con- 
trol of the work. 

On account of the complex composition of the bitu- 
mens and their peculiar physical properties, tests of the 
kind ordinarily applied to engineering materials can- 
not be employed in judging asphalt mixtures, and the 
testing of the materials has been left for the most 
part to experts employed by the asphalt companies. In 
only a few instances have specifications looking to the 
control of the work by test and inspection been em- 
ployed. The specifications used in Kansas City by 
City Engineer Harper in 1908 contain the following 
requirements for the asphalt cement: 

"The asphaltic cement when considered apart from the 
mineral matter shall have the following characteristics: 

" It shall be free from water or decomposition 
products. 

"The various hydrocarbons composing it shall be 
present in homogeneous solution, no oily or granular 
character being present. 

"It must, when tested at 77 F., have a penetration 
of from 3 to 9 millimeters when tested for 5 seconds with 
a No. 2 needle weighted with 100 grams, according to 
the nature of the asphalt and the conditions under 
which it is employed. It must not be so susceptible 
to changes of temperature that if at $2° F. it shows a 
hardness indicated by I millimeter penetration, at 
151 F. it will not be so soft as to give more than 35 
millimeters penetration, using the above method of 
testing. 

" Twenty grams of it shall not lose more than four (4) 
per cent in weight upon being maintained at a uniform 
temperature of 325 F. for seven (7) hours in a cylin- 



242 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

drical vessel two and one-half (2 J) inches in diameter 
by two (2) inches high. 

"Twenty (20) grams of it shall not lose more than 
eight and one-half (8 J) per cent upon being maintained 
at a temperature of 400 F. for seven (7) hours in a 
cylindrical vessel two and one-half (2 J) inches in 
diameter by two (2) inches high. 

" It shall be soluble in chemically pure carbon bisul- 
phide at air temperature to the extent of at least ninety- 
five (95) per cent. 

" It shall not contain of carbonaceous matter insol- 
uble in chemically pure carbon bisulphide, air tem- 
perature, more than four and one-half (4 J) per cent. 

"It shall be soluble in 87 Baume petroleum naph- 
tha, air temperature, to the extent of not less than 
sixty-five (65) per cent and not more than eighty (80) 
per cent. 

"Its solubility in carbon tetrachloride shall not be 
more than one and one-half (1^) per cent less than its 
solubility in carbon bisulphide — both tests being 
made at air temperature. 

" It shall show of fixed carbon not more than fifteen 
(15) per cent. 

"It shall show a flashing point (New York State 
Closed Oil Tester) of more than 350 F. 

"It shall not contain more than three (3) per cent 
of parafin scale, the Holde method of determining 
parafin scale being used. 

" The bitumen entering into the composition shall 
have been in use in the street paving industry under 
conditions similar to those contemplated in this con- 
tract, at least 4 years prior to the letting of this con- 
tract." 



BITUMINOUS PAVEMENTS. 243 

Art. 59. Construction of Sheet Pavements. 

The construction of asphalt pavements in this 
country is, in the main, in the hands of two or three 
large corporations, and methods of construction vary 
but little, the differences in the various pavements being 
principally due to differences in the composition of the 
materials used. 

FOUNDATION. 

Concrete base. As a sheet asphalt surface has no 
power to sustain loads, acting only as a wearing sur- 
face, which must be held . in place from below, it is 
essential that it be placed upon a very firm, unyielding 
foundation. It is consequently nearly always placed 
upon a concrete base, which is commonly formed of 
hydraulic cement mortar and broken stone, prepared 
as described in Art. 47. In the use of this base, it is 
necessary that the mortar be fully set, and the concrete 
thoroughly dry before the asphalt is laid upon it, as 
the placing of the hot surface material upon a damp 
foundation will cause the blistering and possible dis- 
integration of the surface by the steam generated from 
the base by the heat of the material. 

For moderate or heavy traffic in cities, the concrete 
base is commonly made 6 inches thick. For lighter 
traffic a less depth, 4 inches or 5 inches, is sometimes 
employed. The depth necessary will depend upon the 
nature of the road-bed as well as the weight of the 
traffic. It should be greater as the subsoil is less firm 
and well drained. 

Bituminous base. Sometimes a base has been used 
consisting of a layer of broken stone four or six inches 
thick rolled into place and coated with asphalt or coal 



244 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

tar paving cement. This is known as a bituminous 
base. The advantage which has been claimed for it is 
that the foundation and surface material become 
joined into a single mass, with the effect of anchoring 
the surface and preventing the formation of weathering 
cracks and wave surfaces, which are sometimes found 
when the hydraulic base and light surface layer are 
employed. The hydraulic base is commonly preferred 
to the bituminous base, which is practically obsolete, 
because it forms an unyielding structure, not likely to 
be forced out of place by the weight of traffic at any 
point where the support of the road-bed may be 
weakened. 

Macadam base. In surfacing streets with asphalt 
which have previously been macadamized, it is some- 
times possible to use the old macadam as a base for the 
asphalt. This offers a good base in so far as it can be 
used without disturbance. It is difficult, however, to 
change the grade or reduce the crown without destroy- 
ing the bond of the macadam. Old brick and stone 
pavements may also be used in the same way, where 
they can be used without disturbing them. 

BINDER COURSE. 

An intermediate layer known as the binder course is 
now commonly placed between the base and surface 
layer. This layer is ordinarily about i^ inches thick 
and consists of broken stone, which passes through a 
I inch screen, mixed with sufficient bitumen to thor- 
oughly coat the pieces of stone. The paving cement 
used in making the binder course should be of softer 
consistency than that used in the surface material, 
about 3 per cent of bitumen being usually required. 



BITUMINOUS PAVEMENTS. - 245 

The materials are mixed hot, laid and rolled in the 
same manner as the surface layer. This binder becomes 
consolidated with and gives added depth and strength 
to the surface, thus preventing the cracks and wave 
surfaces which may otherwise appear. The binder, as 
commonly formed of broken stone, is open and porous, 
but in some instances stone of graded sizes and sand 
are employed to make a dense bituminous concrete. 
This is desirable practice, adding materially to the 
strength of the pavement under heavy traffic. It 
requires a larger amount of bitumen (about 5 per cent 
to 6 per cent) on account of the larger surface area of 
grains to be coated. 

The binder course has, in some instances, been 
replaced by a coating of asphalt paint, consisting of 
asphalt cement dissolved in benzene. The surface of 
the hydraulic base is painted with this mixture, which 
serves to cement the base to the surface layer. 

After the completion of the hydraulic base and when 
it has stood a sufficient length of time to harden and 
dry out, the binder course is placed and compacted. 
The binder is spread to uniform thickness over the 
base by use of shovels, all of the material being shoveled 
over m order to secure uniform compactness. It is 
then smoothed with rakes having long tines, and after 
partially cooling rolled with a 5 or 6 ton roller. 

SURFACE COURSE. 

Transportation. The materials for the binder and 
surface of asphalt pavements must be carried from the 
mixing plant to the street in some form of truck or 
wagon which will admit of the materials being delivered 
with small loss of temperature. Some form of dump 



246 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

wagon is commonly employed for this purpose, carrying 
from 2 to 4 tons of the materials at a load. The loss 
of heat is not rapid when the material is carefully 
handled and properly protected by tarpaulins, and the 
temperature of the mass should not be reduced more 
than about 10 degrees, where transportation to the 
street takes 2 or 3 hours. 

Placing. As soon as the rolling of the binder course 
has been completed, it is ready for the surface layer. 
This is usually i\ to I J inches thick where a binder 
course is used, or 2 to 2 J inches in single course work. 
The surface material is distributed by hot shovels from 
the piles into which it is dumped from the wagons, all 
the material being handled over as in the case of the 
binder. It is then spread into a smooth layer of proper 
thickness, with hot rakes, all lumps being broken and 
the material loosened up so that under the roller it 
may compact to a uniform density. After raking 
smooth, the surface is rolled with a steam roller. A 
light roller (2 to 4 tons) is commonly used for the first 
rolling until the material is sufficiently compact to 
bear the heavier one (usually weighing 6 to 8 tons), 
which completes the shaping of the pavement. A 
coating of dust, usually hydraulic cement, is given to 
the surface before the final rolling. This gives proper 
color to the surface. 

The handling of the material necessarily varies some- . 
what with its character and requires, for good results, 
skill and experience on the part of the men in charge 
of the work. It is highly important that the material 
be so evenly distributed as to give a surface of uniform 
density; otherwise the surface may compress unequally 
under the traffic, becoming uneven and wavy. It is 
also necessary that the rolling be carefully done in 



BITUMINOUS PAVEMENTS. 2^7 

order to properly compress the asphalt and bring the 
surface to the required form. When the surface is 
rolled out of shape through careless handling, it is 
difficult to bring it back again. The roller must be so 
balanced as to distribute the weight uniformly, a 
pressure of 200 to 300 pounds per linear inch of tire 
being required for the ultimate compression of the 
asphalt surface. 

Rock asphalt. Pavements of rock asphalt are con- 
structed in the same manner as those from free bitumen. 
The rock asphalt makes a harder surface and is more 
slippery than that made from free bitumen. It has 
never come so extensively into use in the United 
States. In Europe, where rock asphalt is very exten- 
sively used, pavements made from free bitumens mixed 
with sand are frequently denominated artificial asphalt 
as distinguished from asphalt or natural asphalt, by 
which is meant the rock found impregnated with 
bitumen. 

In the European rock asphalt pavements the binder 
course is not so commonly employed as in the United 
States, and in many cases the finishing of pavement is 
by means of tampers and smoothing irons instead of 
rollers, the compression given to the surface not being 
so great, ultimate compacting being accomplished by 
the traffic. At the edges of the pavement and in places 
which cannot be reached by the roller, small hand tools 
such as hot smoothing irons and tampers are employed 
for finishing the surface. Sometimes also where the 
rolling has failed to compress the pavement into proper 
surface, it may be necessary to soften the surface with 
smoothing irons in order to reduce it to the required 
form. 



248 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 60. Asphalt Blocks. 

Asphalt paving blocks are frequently formed of a 
mixture of asphalt cement and crushed stone. The 
stone used is mainly trap, or granite, broken so as to 
pass a J inch screen. In early work, limestone was 
used; this was found to lack durability on account of 
the softness of the stone. The mixture is similar to 
that used for the surface of a sheet pavement, containing 
about 8 per cent to 1 1 per cent of asphalt cement, 
7 per cent to 10 per cent limestone dust, and crushed 
stone 80 per cent to 85 per cent. 

The materials are heated to a temperature of about 
300 F., and mixed while hot in an apparatus arranged 
to secure the even distribution of the ingredients 
through the mass. The thorough incorporation of the 
various materials in the mixture is of first importance 
in producing homogeneous and uniform blocks, while 
the quality of the materials used needs as careful 
inspection as in the case of the surface material for 
sheet pavements. 

When the mixing is complete, the material is placed . 
in moulds and subjected to heavy pressure, after which 
the blocks are cooled suddenly by plunging into cold 
water. 

These blocks have usually been made larger than 
paving-bricks, the common size being 12 inches long, 
3 or 4 inches wide, and 4 or 5 inches deep. They are 
laid in the same manner as brick, as closely in contact 
as possible, and driven together. Under the action of 
the sun and the traffic, the asphalt blocks soon become 
cemented together through the medium of the asphaltic 
cement, and form, like the sheet asphalt pavements, a 
practically impervious surface. They are often laid 



BITUMINOUS PAVEMENTS. 249 

upon gravel base, although in the best work a light 
concrete foundation is employed. 

In forming the asphalt block pavement the road-bed 
is brought to subgrade in the ordinary manner and 
rolled, leaving room for the pavement of uniform thick- 
ness to be placed upon it. A layer of gravel 4 or 5 
inches deep is then placed and rolled, or a base of con- 
crete is formed, with a cushion coat of sand I to 2 
inches, and then the paving blocks. The blocks are 
pressed together in the courses by the use of a lever, 
and the courses driven against each other with a maul 
to reduce the joints as much as possible. A coating 
of sand is given to the surface of the pavement, and it 
is rammed to a firm and uniform surface, as in the case 
of brick. 

These blocks have the advantage over sheet asphalt 
for the smaller cities, that the blocks may be formed 
at a central point and shipped ready-for use to the site 
of the proposed pavement, and that no special plant 
need be erected in each town where they are to be 
constructed. They have given satisfaction in use, and 
have frequently shown good durability in wear under 
moderate traffic. It is claimed that they are less 
slippery and may be used upon steeper slopes than 
sheet asphalt. The cost of transportation of the 
blocks makes this pavement expensive in many locali- 
ties not in close proximity to the place of manufacture, 
and prevents them from competing successfully with 
other pavements. 

Art. 61. Maintenance of Asphalt Pavements. 

To give good service asphalt pavements must be 
kept clean. On account of the smooth surface and 
absence of joints, cleaning may be readily accomplished; 



250 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and the presence of dirt, especially in wet weather 
when it is likely to cause the surface to remain damp, is 
liable to cause the asphalt to rot. More than any 
other pavement, therefore, the durability and wear of 
an asphalt surface depends upon its cleanliness. The 
presence of dir,t upon asphalt in damp weather is also 
important in its effect upon the slipperiness of the 
pavement. 

Small repairs of any breaks that may occur in an 
asphalt surface may be easily made, and such repairs 
should be constantly attended to in order to keep the 
surface in good condition. Small breaks will rapidly 
extend if they are not repaired at once. In making 
repairs to the surface of the pavement it is necessary to 
cut away the surface for a short distance about the 
imperfect spot, stripping the surface from the founda- 
tion and cutting the layer down square at the edges, 
after which a new piece of surface may be introduced 
to fill the hole in the same manner that the original 
surface was constructed. Such a patch may ordinarily 
be put on so as to make joints that will join perfectly 
with the old pavement and not show where it has been 
placed. When a surface has become so worn that 
patches would be numerous, the old surface may be 
stripped off and a new one placed upon the original 
foundation. When repairs are to be made upon a 
pavement having a bituminous base it is more difficult 
to cut out the holes in satisfactory shape, as there is 
no well- defined joint between the base and the surface 
layers. 

The repairs that may be required upon an asphalt 
pavement depend, of course, upon the solidity of con- 
struction and the nature of the surface material. There 
is so great variation in the materials employed for the 



BITUMINOUS PAVEMENTS. 251 

wearing surface that, as would naturally be expected, 
very considerable difference in wear is shown by dif- 
ferent pavements. 

It is common to require contractors for asphalt 
pavements to guarantee the pavement for a period of 
years, making all necessary repairs and leaving the 
work in good condition at the end of the period. This 
makes it an object for the contractor to do good work, 
and may sometimes be the most effective way of secur- 
ing it where so many elements of uncertainty enter. 
In general, it is not desirable to require contractors to 
guarantee paving for a long period on account of 
limiting competition and increasing unnecessarily the 
cost of the work. With asphalt paving, however, 
many engineers consider the difficulty of control during 
construction, under ordinary circumstances, such as to 
make a guaranty necessary, while the fact that the 
material is for the most part controlled by a few large 
companies renders the guaranty less undesirable as 
restricting competition. This method has, however, 
been found unsatisfactory in many instances, on account 
of the difficulty of enforcing the guaranty. 

The cost of maintenance of asphalt pavements varies 
widely in different places, depending upon the character 
of the construction used and the local conditions sur- 
rounding the pavement. In Washington, D. C, the 
average life of the surface before renewal is about 20 
years, while the annual cost of maintenance is about 
2.5 to 2.8 cents per square yard per annum. In loca- 
tions where the surface is kept continuously damp, 
particularly if it is not kept clean, the asphalt is apt to 
deteriorate rapidly and, in some instances, scales off 
and gradually disintegrates. The resistance of asphalt 
to water action depends very much upon the density 



252 A TEXT-BOOK ON ROADS AND PAVEMENTS 

of the surface mixture and the ease with which water 
may penetrate it. Great care should be used in laying 
pavements where moisture conditions are not good to 
secure a dense surface mixture in which the voids are 
well filled. Where water may continuously run in the 
gutters, it is usually better to construct the gutters of 
other material less affected by the action of water. 

Injury to asphalt surfaces from illuminating gas 
escaping from leaking mains has been observed by Mr. 
A. W. Dow at Washington, D. C. The heavy hydro- 
carbons of the gas are absorbed by the bitumen of 
asphalt, which is thereby softened and caused to cut 
and flow under the traffic. 

The cost of maintenance depends largely upon the 
system employed in the maintenance work. In some 
cities repairs are made only at considerable intervals 
when the surface is in bad condition, and in such 
instances the ultimate cost is usually much larger than 
where small repairs are made as they are needed to keep 
the surface always in good condition. 

Art. 62. Bitulithic Pavement. 

The name " bitulithic " is commonly applied to a 
pavement, the surface of which is composed of a 
bituminous concrete, the aggregate being a mixture of 
several sizes of broken stone, so proportioned as to 
give a dense material with a small percentage of voids. 
Pavements of bituminous concrete have been occasion- 
ally constructed for a number of years, but the intro- 
duction of this type of pavement upon a considerable 
scale began about 1901, when exploited under a patent 
of the Warren Brothers, and most of those since con- 
structed have been under this patent. 



BITUMINOUS PAVEMENTS. 253 

In the construction of pavements of this class the 
crushed rock is screened into several sizes, which are 
then mixed together in such proportions as to produce 
an aggregate with very small percentage of voids. 
Four to six screens are used, varying from about I J 
inches to -jV inch openings. Sufficient quantities of the 
smaller sizes are employed to fill the interstices in the 
larger sizes; the relative proportions being determined 
in each instance by experiment upon the particular 
material in use. "After the proportions have been 
determined, the mineral material is passed through a 
rotary screen which separates it into several different 
groups of sizes. The proper proportion by weight of 
each of these sizes is secured by the use of a scale having 
seven beams, the exact required amount being weighed 
out and run into a double shaft rotary mixer. There 
it is combined with a bituminous cement which is also 
accurately weighed in the proper proportion. The 
whole is then thoroughly mixed together and dumped, 
while still hot, into carts, hauled to the street, spread, 
and thoroughly rolled with heavy steam road rollers. 

"After the surface is thoroughly rolled, a flush coat 
of quick drying bituminous cement is applied to the 
surface. There is then applied a thin layer of hot 
finely crushed stone, varying from J to f inches in 
size, according to the roughness of the surface desired. 
The pavement is again heavily rolled, leaving the street 
in a finished condition. " 

These pavements are commonly constructed upon 
bituminous foundations (see Art. 48). When the sub- 
foundation is not firm, and concrete foundations are 
required, the surface of the concrete is roughened by 
scattering stone of about I \ inch diameter lightly over 
it, and ramming the stones into the concrete to about 



254 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

half their depths. This forms a bond between the base 
and surface of the pavement, and prevents the creeping 
of the surface. 

These pavements have been used with good success 
in many places throughout the United States. They 
require care and skill in construction, both in securing 
proper grading of the mineral aggregate and in the 
character and proportions of the bituminous cement. 
It is claimed by the advocates of this kind of construc- 
tion that, on account of the density and firmness of the 
mass of stone of which they are composed, a softer 
bitumen may be employed, thus eliminating the danger 
of cracking in cold weather. In some instances, where 
hard stone has been used in forming the surfaces, there 
are indications that this construction will give better 
resistance to wear than the ordinary asphalt surface, 
but longer experience is necessary to fully test its 
durability. It has been successfully used upon much 
steeper grades than sheet asphalt, being reported as 
affording a good foothold to horses, and satisfactory 
in one instance upon a 12 per cent grade. 

In constructing these pavements, as with sheet 
asphalt, it has been customary to rely upon the con- 
tractor's guaranty for securing good work and no 
attempt is usually made to determine the character of 
the bituminous cement by direct tests. This is an 
undesirable feature of most work with these materials, 
and it is to be hoped that, as better information con- 
cerning the bitumens becomes available, more satis- 
factory specifications may become feasible. The fol- 
lowing is an extract from the specifications used in 
St. Louis in 1908: 

"Upon the foundation shall be laid the wearing 
surface, which shall be composed of carefully selected 



BITUMINOUS PAVEMENTS. 255 

sound, hard crushed stone, mixed with bituminous 
cement and laid, as hereinafter specified. 

" The stone last referred to shall have a percentage of 
wear not to exceed 5 per cent when tested in the follow- 
ing manner: 

" The sample to be tested shall be broken into pieces 
that will pass, in all positions, through a 6 centi- 
meter ring, but not through a 3 centimeter ring. The 
fragments of stone shall then be cleaned, dried in a hot 
air bath at 1 00° C. and cooled in a dessicator, after 
which five kilograms shall be weighed out and placed 
in a cylinder of an abrasive machine and the cover 
bolted on. This machine (see Art. 37) shall consist 
of a cast iron cylinder, or cylinders, fastened to a shaft 
so that the axis of each cylinder makes an angle of 
30 degrees with the axis of rotation. Each cylinder 
shall be 20 centimeters in diameter and 34 centimeters 
in depth; shall be closed at one end and shall have a 
tightly fitting cover at the other end. After this, 
the machine shall be rotated at the rate of 2000 revo- 
lutions per hour for five hours. When the 10,000 
revolutions of the machine are completed, the contents 
of the cylinder shall be placed on a sieve of 0.16 centi- 
meter mesh, and the" material which passes through 
carefully collected and weighed. The ratio between 
the weight of the fine material and the original five 
kilograms placed in the cylinder is the percentage of 
wear. 

" After immersion in water for a period of ninety-six 
hours, a smoothly worn fragment of stone weighing 
between 20 and 60 pounds shall not absorb more than 
3 pounds of water per cubic foot of stone. 

"After heating the stone in a rotary mechanical 
dryer to a temperature of about 250 F. it shall be 



256 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

passed through a rotary screen having six or more 
sections, with varying sized openings, the maxi- 
mum of which shall not be larger than one and 
one-half inch, and the minimum one-tenth of an inch 
in diameter. The several sizes of stone thus separated 
by the screen sections shall pass into a bin containing 
six sections or compartments. From this bin the 
stone shall be drawn into a weight box, resting on a 
scale having seven beams. The stone from each bin 
shall be accurately weighed in the proportions deter- 
mined by laboratory tests that will give the greatest 
density of mineral aggregate and the greatest inherent 
stability of the mineral aggregate. From the weigh- 
box each batch of mineral aggregate composed of 
different sizes, accurately weighed, as above described, 
shall pass into a ''twin pug" or other appropriate 
form of mixer. If the proportions of crushed stone in 
the mixer do not provide enough fine particles to bring 
the aggregate to the density desired, there may be 
added not to exceed 15 per cent of fine sand, gravel, 
hydraulic cement, and pulverized limestone. To the 
stone in the mixer shall then be added a sufficient 
quantity of Warren's Puritan Brand No. 21 Bituminous 
Water-proof Cement, to thoroughly coat all the particles 
of stone and fill all the voids in the mixture. The 
bituminous cement shall, before mixing with the stone, 
be heated to between 200 and 250 F. and the amount 
used in each batch shall be accurately weighed and 
used in such proportion as have been previously deter- 
mined by laboratory tests to give the best results 
and fill the voids in the mineral aggregate. The 
mixing shall be continued until the result is a uniform 
bituminous concrete. In this condition it shall be 
hauled to the street and there spread on the prepared 



BITUMINOUS PAVEMENTS. 257 

foundation to such depth that after thorough com- 
pression with a steam roller it shall have a thickness 
of two inches. The proportion of the various sizes of 
stone and of bituminous cement shall be such that the 
compressed mixture shall have as nearly as possible 
the density of solid stone. 

"After rolling the wearing surface, there shall be 
spread over it a thin coating of Warren's Quick 
Drying Bituminous Flush Coat Composition in a plas- 
tic condition, for the purpose of closing any pores or 
cellular openings, and to thoroughly fill any uneven- 
ness or honeycomb which may appear in the surface. 
There shall then be applied thereto and combined 
therewith while plastic, stone chips, with the same 
qualities required of the stone in the pavement 
proper, by rolling the same into the surface with 
a heavy steam roller for the purpose of presenting a 
gritty surface. 

"In order to get the greatest possible density, the 
pavement shall be rolled continuously from the time the 
bituminous concrete is brought upon the street until 
the stone chips have been rolled into the surface and 
the roller no longer makes a perceptible impression 
upon the pavement, 

" Each layer of the work shall be kept as clean as 
possible so as to readily unite with the succeeding 
layer. The bituminous compositions shall in each 
case be free from water, petroleum oil, water gas, or 
process tars and shall be especially refined with a view 
of removing the light oil, naphthaline and other crys- 
talline matter susceptible to atmospheric influences." 



CHAPTER IX. 

WOOD-BLOCK PAVEMENTS. 
Art. 63. Types of Wood-Block Pavement. 

The use of wood blocks for the surfaces of pave- 
ments began a little before 1840, and since that time 
many types of construction have been tried with vary- 
ing degrees of success. The first pavements in London, 
in 1839, consisted of hexagonal blocks of fir, six to 
eight inches in diameter and about six inches deep, 
placed on a base of gravel. In 1841 a pavement of 
round beech blocks was laid upon a foundation of 
planks and sand. The wood soon decayed and the 
pavement was removed. 

In Philadelphia, square hemlock blocks were laid in 
1839 and hexagonal hemlock blocks probably a little 
earlier. Both were quickly destroyed by the decay of 
the blocks. In New York and Boston similar pave- 
ments were constructed at about the same time and 
with much the same result. 

In 1855 a pavement of tamarac blocks was laid in 
Quebec, This pavement was placed upon a base 
formed of a flooring of one and one-half inch boards 
laid longitudinally and crossed at right angles by a 
second flooring of inch boards. A layer of sand one- 
half inch thick was placed over the boards. The 
tamarac blocks were ten to fifteen inches in diameter 
and twelve inches long, small pieces of wood being 
forced into the spaces between the blocks. The 

258 



WOOD-BLOCK PAVEMENTS. 259 

joints were filled with a mixture of sand, cement, and 
tar. This heavy construction is reported as having 
given very good wear, with no decay. 

Cedar Block Pavements. In the earlier wood pave- 
ments of the United States, cedar blocks were com- 
monly employed. These blocks were used in the form 
of whole sections of the tree on account of the liability 
of the wood to split off between the layers when cut to 
a rectangular shape, as well as to reduce waste to a 
minimum. They usually varied from 4 to 9 inches in 
diameter and 4 to 8 inches in depth. In some cases 
the blocks were cut to a true cylindrical form, the sap- 
wood as well as the bark being cut away by passing 
the block through sets of knives, gauged to turn out 
true cylinders of given size. The use of sapless blocks 
increases the life of the pavement by augmenting the 
resistance of the material both to the wear of traffic and 
to the disintegrating influences of the atmosphere. 

These pavements were usually placed upon a founda- 
tion of boards laid upon sand. The planks were com- 
monly tarred and laid lengthwise of the street, being 
nailed to scantling or other boards placed across the 
street and bedded in the sand. This construction has 
the disadvantage of lacking firmness as well as of being 
perishable, although in some instances good results have 
been obtained by its use. 

The construction of a pavement of this type is shown 
in Fig. 25. Blocks of ' varying sizes are employed, 
being set in contact with each other in such a way as 
to leave the spaces between the blocks as small as 
possible. Usually the joints are filled with sand and 
gravel, sometimes with a coating of tar; or in some 
cases the joint is partially filled with tar and then com- 
pletely filled with sand or small gravel. When the 



260 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

ordinary coal-tar paving cement filling is used, the 
joints are first filled nearly full of sand or gravel, which 
is pounded down with a bar, after which the hot cement 
is poured in until the joint is well filled. 

These pavements, on account of the plentiful supply 
of timber were constructed for very low first cost and 
undoubtedly served a very useful purpose in many 
instances, permitting the improvement of many streets 
to an extent which at that time would have otherwise 
been impossible. They lifted the streets out of the 
mud, although the pavements did not usually last long 




Fig. 25. 

and were afterward replaced by more durable materials. 
Pavements of this type wear rapidly under traffic, soon 
becoming uneven, and their use has, for the most part, 
been discontinued on account of their lack of economy. 
Nicholson Pavement. Rectangular wooden blocks 
set like the cedar blocks, upon a plank foundation were 
at one time quite extensively used and known as 
Nicholson pavements. In these pavements the blocks 
are set with their longest dimension transverse to the 
length of the street. They are usually arranged in 
courses across the street, being placed close together 
in the courses, and arranged to break joints in adjoining 
courses. Between courses a joint is usually made £ to 



WOOD-BLOCK PAVEMENTS. 



26l 



\ inch in width for the purpose of affording a foothold 
to horses. In the older pavements of this character a 
much wider joint was employed, some as much as an 
inch in width, with the idea that they were necessary 
to secure proper foothold. The joints were filled in the 
same manner as in the round block pavement. These 
pavements like the cedar blocks have given place for 
the most part to more economical kinds of construction. 
Rectangular Blocks on Concrete. The use of a concrete 
base under a surface of the Nicholson type effected a 
marked improvement in the wear of the pavement. 




Fig. 26. 

Round block pavements were also sometimes placed 
upon a concrete foundation. 

In using a concrete foundation a cushion coat of 
sand is commonly employed on top of the concrete in 
which to bed the blocks in order that they may be 
brought to an even surface. Sometimes a thin layer 
of cement mortar is used in place of the sand upon the 
concrete; and in London some pavements have been 
constructed with a thin layer, about J inch, of asphalt 
mastic over the concrete, the blocks resting upon the 
mastic. 

A pavement of this type is shown in Fig. 26. 

In laying a pavement of this kind a course of blocks 



262 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

is first set across the street, and then a strip of wood 
of the thickness of the joint is set against the row of 
blocks and left until the next course is placed, or 
sometimes spuds with heads of the thickness of the 
joints are driven to the head in the side of each block, 
and the next row of blocks are set against the spuds. 

In some pavements of this kind hydraulic cement 
is employed in filling the joints, and in some instances 
the lower half of the joint is filled with coal tar paving 
cement and the upper half with hydraulic cement 
mortar. The cement mortar gives a harder wearing 
surface, and protects the pitch from the softening action 
of the sun in warm weather. In later practice the 
width of joint has been gradually reduced until the 
blocks are set in contact with each other, occasional 
expansion joints being provided. 

These pavements have been extensively used in 
England, and to a smaller extent in the United States. 
They have been fairly satisfactory in use but have 
been, for the most part, superseded by treated blocks. 

Treated Block Pavement. Wood blocks treated by 
some preservative process for the purpose of preventing 
decay and of hardening the block so as to give better 
resistance to wear have come into use somewhat 
extensively since about 1900. These pavements have 
given good service in use. They are rather expensive 
in first cost, but have in some instances been found 
durable under heavy traffic and are fairly economical. 

Art. 64. Wood Blocks. 

Wood-block pavements are constructed of blocks set 
with the fibers vertical, so that wear comes upon the 
ends of the fibers and has no tendency to split pieces 



WOOD-BLOCK PAVEMENTS. 263 

off from the blocks. These blocks are usually from 6 
to 12 inches in length, 3 to 4 inches in width, and 3 to 5 
inches in depth. Some engineers require the blocks to 
be of uniform length but a variation of from about 6 to 
10 inches is more common and seems desirable because 
of the greater freedom in obtaining timber for the 
purpose. A depth of 3i inches, or at most 4 inches, is 
sufficient and there seems to be no advantage in greater 
depth, as the block would become unserviceable and 
need to be renewed before this depth would be worn 
away. The blocks are cut from planks of uniform 
thickness, and are set in courses across the street, the 
blocks in adjoining courses breaking joints with each 
other. 

Kinds of Wood. Wood for pavements should be 
close-grained and not too hard. It should be as homo- 
geneous as possible in order that the wear may be 
uniform, and soft enough that it may not wear smooth 
and slippery. To give good service in wear the wood 
should be penetrated by water as little as possible and 
show good resistance to decay under the action of the 
weather. 

Wood for this use should be sound and well seasoned. 
The blocks should always be subjected to careful in- 
spection. All sapwood needs to be removed in order 
to lessen the liability to early decay, and blocks con- 
taining shakes and knots should be rejected. 

In Australia hard-wood blocks have been quite 
extensively used and are reported as giving good 
service, although they are admitted to be somewhat 
slippery in wet weather. Australian Karri and Jarrah 
woods are employed, and it is claimed for them that 
they show unusually great resistance to wear and are 
not soon affected by decay. 



264 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In London, where wood pavements have been very 
extensively employed, Swedish yellow deal is com- 
monly placed at the head of the list of woods in value, 
yellow pine and Baltic fir being also largely used and 
considered good in use. The Australian woods above 
mentioned have also been used to some extent in Lon- 
don, and are said to have given very satisfactory ser- 
vice, showing greater resistance to wear than deal or 
pine, although somewhat expensive. Deal treated with 
creosote is extensively used and seems to give the best 
satisfaction. In Paris, teak, karri, and pitch pines are 
frequently employed, although treated native pines are 
more commonly used and have been found to give 
good service. 

In the United States the introduction of these pave- 
ments has been limited by the high cost of suitable 
timber, and its extension is largely dependent upon 
obtaining satisfactory materials at lower cost. South- 
ern long-leaf yellow pine has been most extensively 
employed, but is so much in demand for other purposes 
that properly selected timber for the purpose is too 
expensive. Norway pine, tamarac, and fir are also used 
for paving blocks to some extent. Experiments upon 
the Southern black gum have seemed to indicate that 
it may be used to advantage when properly treated. 
This wood is less valuable for other purposes, as it has 
a tendency to warp and is subject to decay, and is 
being used for paving to considerable extent. The 
gum, being subject to decay, needs to be properly treated 
in order to satisfactorily resist wear in a pavement. 

The specifications used for blocks in New York City 
are as follows : 

'The material to be treated shall be wood blocks, 
which may be either of Southern long-leaf yellow pine, 



WOOD-BLOCK PAVEMENTS. 265 

Southern black gum, Norway pine, or tamarac, not 
less than 90 per cent of heart, of a texture permitting 
satisfactory treatment as hereinafter specified, and is 
to be subject to inspection at the works in the stick 
before being sawed into blocks. 

"All blocks shall be of sound timber free from bark, 
loose or rotten knots, or other defects which would be 
detrimental to the life of the block or interfere with its 
laying. No second growth timber will be allowed. 

"The paving blocks cut from the lumber above 
specified shall be well manufactured, truly rectangular 
and of uniform dimensions. Their depth (parallel to 
the fibre) shall be three and one-half (3^) inches. 
Their length shall be not less than six (6) nor more than 
ten (10) inches, and their width shall be not less than 
three (3) nor more than four (4) inches, but all blocks 
used in any one contract are to be of the same width 
and of the same timber. Their depth and width shall 
not vary more than one-eighth (I) inch from the 
dimension specified for any one contract/' 

Art. 65. Treatment of Wood Blocks. 

The most serious objection commonly raised to the 
older type of wood pavement is that wood, being porous, 
absorbs moisture readily, and is thus liable both to 
destruction through decay and to become injurious to 
health. Various methods were therefore proposed 
for rendering the blocks less pervious and more durable 
by impregnating them with various substances which 
fill the pores and act as preservatives. The earlier 
attempts in this direction were not in the main success- 
ful and little seemed to be gained in durability by the 
treatment. Solutions of mineral salts were tried but 



266 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

were found unsuitable for the purpose. Creosoting the 
blocks, which consists in impregnating the wood with 
the oil of tar, or creosote, was more successful, but 
with the type of construction in use seemed of doubt- 
ful economic value. In this process the wood is 
first thoroughly dried, usually by heating it in a kiln, 
and the hot creosote is then forced in under pressure. 
The method of accomplishing this varies in different 
places. In order to be effective the process must be 
thoroughly carried out and the pores well filled. It has 
been commonly recommended that from 8 to 12 pounds 
of creosote per cubic foot of timber should be forced in, 
as a minimum requirement for the softer woods, such 
as are commonly used in pavements. Creosote has the 
property of destroying the lower forms of animal life, 
and is therefore an effective preservative against 
destruction through these agencies where they exist. 
This method is therefore often employed for the 
preservation of timber for subaqueous construction in 
sea-water. 

This process, when properly applied, is effective in 
preventing decay, and therefore in lengthening the 
natural life of the wood. It also renders the wood 
practically impermeable, and thus removes the objec- 
tion to the pavement based upon its absorbent ^nature. 
It does not, in general, appear to increase the resistance 
of the wood to the wear of the traffic, and in most cases 
the advantage to be gained seems so small as to render 
its economic value for this purpose at least doubtful. 

In more recent practice, the treatment has been 
directed to the hardening of the block as well as the 
prevention of decay. This has been accomplished by 
modifying the character of the material with which the 
wood is impregnated through the introduction into 



WOOD-BLOCK PAVEMENTS. 267 

the creosote of some substance which hardens in the 
pores of the wood, thus waterproofing the timber and 
hardening its fibres. Experience seems to indicate that 
treatment by the improved methods considerably 
increases the life of the timber and its resistance to 
wear, and this has resulted in a considerable revival of 
the use of wood-block pavements, which had for the 
most part ceased. 

The methods most commonly employed in the 
United States for the treatment of blocks are the 
Kreodone process and the Creo-resinate process. The 
Kreodone process consists in impregnating the blocks 
with an oil derived from creosote oil, which possesses 
the original preservative properties and forms a water- 
proof coating on the exterior of the wood. In the 
Creo-resinate treatment, the wood is impregnated with 
a substance consisting essentially of a mixture of the 
oil of tar with resin, the resin acting as the water- 
proofing and hardening material. The amount of resin 
required varies from about 25 per cent to 50 per cent 
of the mixture, and depends upon the character of the 
oil used, a heavy dense oil requiring less resin than a 
lighter and more volatile oil. The method of treat- 
ment is thus described by Mr. F. A. Kummer:* 
"Blocks, after being cut to size, are placed in circular 
cages made of band steel of approximately the di- 
ameter of the cylinders in which the treatment takes 
place, and are then, while in these cages, run into 
the cylinders on cars. The cylinders themselves are 
usually about 6 feet in diameter and somewhat over 
100 feet long, and are provided with steam coils along 
the bottom and sides to provide heat for drying and 
preparing the lumber for treatment. The blocks are 

* Engineering Record, August 25, 1906. 



26& A TEXT-BOOK ON ROADS AND PAVEMENTS. 

heated in this way, some works employing live steam 
instead of steam coils, and others a combination of the 
two. After several hours both by the use of heat and 
by the use of a vacuum pump, a large portion of the 
moisture and light volatile oils in the wood, if the latter 
contain any such, are driven off. The preservative 
material is run into the cylinder under a vacuum and 
hydraulic pressure of 200 lbs. per square inch, applied 
from two to three hours, or for such longer period of 
time as may be necessary to thoroughly treat the 
charge, the result being accomplished when the gauges 
show that no more material is entering the wood. " 

The specifications for treated blocks used by Mr. 
Tillson in New York City in 1908 are as follows: 

"The blocks are to be treated throughout with an 
antiseptic and waterproof mixture, not more than 75 
per cent of which shall be creosote or heavy oil of 
coal tar conforming to the specifications hereinafter set 
forth. All parts of each individual block shall be. 
thoroughly treated, and not less than twenty (20) 
pounds of the mixture per cubic foot shall be injected. 

"Treated pine blocks shall weigh as much as water. 
Treated gum blocks shall weigh as least 59 lbs. per cubic 
foot and any other wood at least 20 lbs. per cubic foot 
more than the recognized weight of sucn untreated 
blocks. 

"Blocks cut from the several classes of timber 
allowed under these specifications will require different 
manipulation and treatment, and for this reason the 
exact methods of applying the mixture to the several 
timbers named will not be specified, it being understood 
that whatever method is used the process must conform 
in every respect to the best and most advanced knowl- 
edge of the art, the purpose of the city being to allow 



WOOD-BLOCK PAVEMENTS. 269 

the contractors to manufacture specification blocks by 
following any preferred detail and by the use of any 
particular plan or machinery which may be properly 
adapted to secure the results herein required. 

"The creosote oil is to conform to the following 
specifications when tested, as follows: 

"The gravity at 68° F. shall be not less than 1. 12. 
When distilled in a retort with a thermometer sus- 
pended not less than one inch above the oil, it shall 
lose not more than thirty-five (35) per cent up to 315 
degrees Centigrade, and not more than fifty (50) per 
cent up to 370 degrees Centigrade. The oil is to be 
free from adulteration; it must not be mixed with or 
contain any foreign material. 

"The resin is to be solid resin obtained from pine. 
It is to be reduced to a fine dust by grinding and then 
incorporated with the hot creosote oil in a suitable 
mixing tank until the proper proportions are secured/' 

The specifications employed in St. Louis in 1908 
are as follows: 

"After the blocks have been inspected and found 
satisfactory they shall be placed in an air tight chamber 
where by means of superheated steam and the use of 
a vacuum pump, all sap in the blocks shall be vaporized 
and the moisture in them removed. When the blocks 
are thoroughly dry, and while the cylinder is under 
vacuum of fifteen to twenty inches of mercury, heavy 
creosote oil, of the grades known as Kreodone, or 
Republic Creosote Paving Oil, especially prepared 
for paving purposes, shall be admitted to the cylinder 
and pressure added until the pressure in the cylinder 
shall be at least sixty pounds to the square inch. The 
blocks shall remain in the cylinder until they have 
absorbed twelve pounds of oil per cubic foot of timber 



270 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and until the creosote oil shall have impregnated the 
timber through the entire thickness of the block, and 
to the satisfaction of the Board of Public Improve- 
ments and the Street Commissioner/ 7 



Art. 66. Tests for Wood Blocks. 

Specification requirements for wood blocks vary 
widely in different places throughout the country 
and no systematic method has been adopted for the 
inspection and testing of the blocks. A number of 
tests have been proposed for use both at the plant 
where the blocks are treated and after the blocks have 
been delivered at the site of the pavement. Inspec- 
tion of the blocks is frequently made before treatment, 
as well as tests of the oil to be used in the treatment, 
an inspector being kept at the plant for the purpose 
while the blocks are being prepared. The thoroughness 
of the treatment is determined by the difference in 
weight of treated and untreated blocks. 

For the examination of wood blocks after their 
delivery at the point of use, several tests are in use or 
have been proposed: 

a. The blocks are inspected as to their size, shape, 
and freedom from defects. * " 

b. Blocks may be split and examined as to the 
thoroughness of the treatment, and a weight test 
applied to determine whether a sufficient quantity 
of oil has been absorbed by the block. 

c. Tests of absorption are made by first drying the 
blocks and then soaking them in water, thus deter- 
mining the amount of water that may be absorbed. 

d. The character of the oil with which the block has 
been treated is tested by extracting the oil with carbon 



WOOD-BLOCK PAVEMENTS. 2? I 

bisulphide and then subjecting it to tests to determine 
whether it conforms to the specifications for oil to be 
used in the treatment. The separation of the creosote 
oil from the solution is effected by distillation, the sol- 
vent being first removed at a temperature of about 
120 degrees Centigrade and the creosote oil below 
about 370 degrees Centigrade. 

e. It has been proposed * to test the resistance to 
abrasion of the blocks by grinding them upon a disk 
machine, but no records are available as to results 
obtained in such tests. 

The following extracts show the tests imposed by 
Mr. Tillson in specifications for work in New York 
City in 1908: 

"After treatment the blocks are to show such 
waterproof qualities that after being dried in an oven 
at a temperature of 100 degrees for a period of twenty- 
four hours, weighed and then immersed in clear water 
for a period of twent3^-four hours and weighed, the gain 
in weight is not to be greater than three and one-half 
(3i) per cent. 

"Fine turnings from the block shall be placed in a 
suitable extraction apparatus and the oil completely 
extracted therefrom with ether or carbon bisulphide. 
The oil so extracted shall be placed in a suitable still 
and distilled. The portion up to 120 degrees Centi- 
grade, consisting of the solvent, is to be collected apart. 
The oil shall then be distilled up to 370 degrees Centi- 
grade. The creosote oil thus obtained must conform 
in all respects to the requirements of paragraph 39 
(see p. 269). 

"The Engineer shall have tests and examinations 
made at the contractors' works of the materials and 
* Municipal Engineering, November, 1904, p. 353. 



272 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

blocks proposed to be used, and reject any or all of such 
materials and blocks as he may consider not to be 
in compliance with these specifications. The Borough 
President shall appoint an inspector at the expense 
of the contractor, who shall inspect the lumber and 
other materials used in the manufacture of the blocks, 
and the treatment of the blocks; and he shall reject any 
of such materials and blocks as he may consider not 
to be in compliance with these specifications. 

"The blocks shall be carefully inspected after they 
are brought on the line of work, and all blocks which 
in quality and dimensions do not conform strictly to 
the requirements will be rejected and must be imme- 
diately removed from the line of work." 

Art. 67. Construction of Wood Pavements. 

As stated in Art. 63, the older types of wood-block 
pavement, in which the blocks were laid with open 
joints on a plank foundation or on gravel, are prac- 
tically obsolete, and wood blocks are usually laid with 
close joints upon concrete foundations. This gives 
firm support to the blocks and admits of even wear 
upon the surface of the pavement. A Surable base 
also has the advantage that when the surface layer is 
worn out, the pavement may be resurfaced without 
removing the foundation. The concrete base is con- 
structed in the ordinary manner as described in Art. 47. 
It is commonly about 6 inches thick, although under 
specially trying conditions a somewhat greater thick- 
ness is sometimes employed. In a few of the European 
pavements very heavy foundations, 7 or 8 inches thick, 
are employed; but these are exceptional and the 6 inch 
depth is usually found sufficient. Lighter foundations, 



WOOD-BLOCK PAVEMENTS. 273 

4 or 5 inches in depth may be used under favorable 
conditions and where traffic is not heavy; but these 
pavements are usually employed upon streets of con- 
siderable traffic, and in such situations very light 
construction is not desirable. 

For the purpose of receiving the blocks and affording 
them uniform support, a cushion coat of sand or a 
thin coating of cement mortar is placed over the con- 
crete. The sand cushion when used is usually about 
I inch in thickness and is placed in the same manner 
as in laying a brick pavement. When a mortar surface 
is employed, a coating of about \ inch of mortar is 
floated over the surface of the concrete and brought to 
the exact form of the finished surface, the blocks being 
placed before the mortar sets and bedded into the 
surface of the mortar. This method, while used to a 
much less extent than the sand cushion, seems to give 
excellent results in maintaining a uniform surface 
where the work is properly done, giving more uniform 
support than the sand cushion. 

The blocks are set with the grain vertical, close 
together and commonly in courses making an angle 
of 60 to 70 degrees with the curb line. In some 
instances the blocks are placed with open joints across 
the street of \ to \ inch. Most of the older work was 
constructed in this manner, the wide joints being 
intended to give better foothold to horses, as well as to 
allow for expansion. Experience has shown that 
where impervious joints are secured, the expansion may 
be taken care of by an occasional expansion joint, such 
joints being placed along each curb and across the street 
at distances of 100 to 200 feet, a joint of one-half inch 
every 100 feet being usually sufficient in good work. 
Pavements constructed in this manner have the dis- 



274 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

advantage of being somewhat slippery and wide joints 
are frequently used where the grade of the street is 
more than 3 or 4 per cent. There are, however, in- 
stances of wood-block pavements with close joints on 
gradients of as much as 8 per cent which seem to give 
satisfactory results. 

Three methods of filling joints are frequently em- 
ployed, sand, pitch and cement mortar being used. 
Sand filler is applied by placing a light coating of dry 
sand over the surface and brushing it into the joints, 
then covering the pavement with a layer of sarid and 
opening the street to traffic. Pitch joints are made by 
the use of asphalt or coal-tar paving cement as used 
for brick pavements. They are made by spreading 
the hot paving cement over the surface and brushing 
into the joints. Care must be used to apply the cement 
at such temperature as will cause it to readily run into 
the joints and brush off all surplus cement. A light 
coating of sand is then placed over the pavement to 
take up and grind off the pitch left on the surface of 
the pavement, which may otherwise become objection- 
able in warm weather. 

When the joints are grouted with hydraulic cement, 
a mortar composed of one part cemenlf to two parts 
sand is usually employed, mixed to a liquid condition 
so that it may easily run into the joints. This mortar 
is slushed upon the surface and broomed into the 
joints, and a light coating of sand is placed over the 
surface before opening to traffic. This sand is ground 
by the traffic into the blocks, tending to make the sur- 
face more gritty. 

Following are extracts from the 1908 specifications 
used in the Borough of Manhattan, City of New York: 

"The concrete foundation shall be 6 inches thick, 



WOOD-BLOCK PAVEMENTS. 275 

including a mortar top surface of one-half inch in thick- 
ness, the concrete proper being 5^ inches thick, and 
:shall withstand such tests as the engineer may deem 
necessary, and the contractor shall furnish such samples 
as may be required for the purpose. 

"Upon the surface of the concrete foundation shall 
be spread a bed of cement mortar i inch in thickness. 
This mortar surface shall be composed of a slow setting 
Portland cement, and clean, sharp sand, free from 
pebbles, over one-quarter inch in diameter, and mixed 
in the proportion of one part cement to four parts of 
sand. This mortar top shall be thoroughly rammed 
into place with concrete rammers until all the uneven- 
ness in the concrete shall be taken up, and shall then 
be 'struck' to a true surface, parallel to the top of the 
finished pavement. 

"On the surface of the concrete foundation before 
the mortar bed is laid shall be set strips of wood 4 inches 
wide by \ inch thick, or strips of steel 4 inches wide by 
not less than \ inch thick, and of the greatest length 
convenient for handling. These strips shall be care- 
fully set parallel and about 8 or 10 feet apart, running 
from curb to curb, and be imbedded in mortar through- 
out their length so that the top surface shall be 3 \ 
inches below and parallel to the grade of the finished 
pavement. The space between two strips having been 
filled with mortar, a true and even top surface shall be 
struck by using an iron-shod straight edge on the 
strips as a guide, and as soon as the bed has been struck, 
the strip which would interfere with laying the block 
shall be removed and its place carefully filled with 
mortar with a trowel. 

" If the width of the roadway be such that the laying 
of blocks on a complete section cannot be completed 



2J6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

before the mortar takes its initial set, the strips may 
be placed parallel to the curb, and templates cut to 
the curve of the desired crown shall be used on these 
strips to strike the bed. 

"On this mortar surface, spread and smoothed as 
above to the proper crown and grade, the blocks are 
to be laid with the grain vertical and at such an angle 
with the curb as the engineer may direct. They shall 
be laid in parallel courses with as tight joints as possible, 
each block being firmly bedded in the mortar bed so as 
to form a true and even surface. A \ inch paving 
expansion joint shall be used along each curb and across 
the street every ioo feet. 

"The joints shall then be filled with cement grout 
composed of two parts clean sand and one part Port- 
land cement, mixed to a perfectly liquid form, and the 
surface of the block shall be slushed with same and 
the joints swept until they are completely filled. The 
surface shall then be covered with J inch of screened 
sand." 

Art. 68. Maintenance of Wood Pavements. 

The ordinary maintenance of wood pavements, like 
that of most other pavements, consists in keeping the 
pavement clean and in repairing from time to time any 
small breaks that may appear in the surface due to im- 
perfect material or to the settling of the foundation. 
These repairs would, of course, include the removal of 
any defective blocks and the taking up and replacing of 
any portion which may settle out of surface through 
inefficient support. 

It is generally agreed that the wear of a wood surface 
is improved by giving it an occasional coating of small 
gravel, in some cases two or three times a year, and 



WOOD-BLOCK PAVEMENTS. 277 

permitting it to be ground into the surface for a few 
days. 

When the wood pavement needs renewal or exten- 
sive repairs the surface may be relaid as with any other 
block pavement: if a permanent foundation be em- 
ployed, by stripping the blocks from the foundation and 
placing a new surface in the same manner as the first 
one, with a board foundation that also must be relaid. 
Observations made by Mr. Kummer* seem to indi- 
cate that the continual wetting of a wood block sur- 
face tends to materially reduce the resistance to wear. 
Blocks from a street which had been sprinkled " instead 
of being pounded down and dense and hard, as is the 
case on streets not so sprinkled, had broomed out under 
the action of travel and the preservative material 
mechanically pounded out of the wood by the com- 
bined action of the travel and water. This, of course, 
leaves the surface of the block unprotected by the 
antiseptic preservative and subject to decay. It also, 
in its spongy condition, offers poor resistance to wear. " 
The surface of wood block pavement does not give off 
fine dust, and need only be sprinkled sufficiently to be 
swept clean. For the best results it is necessary that 
the surface should be kept free from dirt. 

* Engineering Record, August 25, 1906. 



CHAPTER X. 

STONE-BLOCK PAVEMENTS. 

Art. 69. Stone for Pavements. 

Stone-bi!ock pavements are commonly employed 
where the traffic is heavy and a material needed which 
will resist well under wear. 

Stone for this purpose must possess sufficient hard- 
ness to resist the abrasive action of wheels. It must 
be tough, in order that it may not be broken by shocks. 
It should be impervious to moisture and capable of 
resisting the destructive agencies of the atmosphere 
and of weather changes. 

Experience only can determine the availability of 
any particular stone for this use. The stone may be 
tested in the same manner as brick, and perhaps some- 
thing predicated as to the probability of its wearing 
well under traffic; but the conditions of the use of the 
material in the pavement are quite different from those 
under which it may be tested, and any testfe looking to 
a determination of its weathering properties are apt to 
be misleading. 

Examination of a stone as to its structure, the close- 
ness of grain, homogeneity, etc., may assist in forming 
an idea of its nature and value for wear. Observations 
of any surfaces which may have been exposed for a 
considerable time to the weather, either in structures 
or in the quarry, will be the most efficient method of 
forming an opinion concerning the weathering proper- 

278 



STONE-BLOCK PAVEMENTS. 2?9 

ties of the stone. The conditions of use in pavements 
are, however, somewhat different from ordinary expo- 
sure in structures, on account of the material in the 
pavement being subject to the action of water contain- 
ing acids and organic substances due to excretal and 
refuse matter. A low degree of permeability usually 
indicates that a material will not be greatly affected by 
these influences and also that the effect of frost will 
not be great. 

Granite and sandstones are commonly employed for 
paving blocks and furnish the best material. Lime- 
stones are sometimes used, but have seldom been found 
satisfactory. Trap-rock and the harder granites, while 
answering well the requirements as to durability and 
resistance to wear, are objectionable on account of 
their tendency to wear smooth and become slippery 
and dangerous to horses. Granite or syenite of a tough, 
homogeneous nature is probably the best material for 
the construction of a durable pavement for heavy 
traffic. Granites of a quartzy nature are usually brittle 
and do not resist well under the blows of horses' feet or 
the impact of vehicles on a rough surface. Those con- 
taining a high percentage of feldspar are likely to be 
affected by atmospheric agencies, while those in which 
mica predominates wear rapidly on account of their 
laminated structure. 

Sandstones of a close-grained, compact nature often 
give very satisfactory results under heavy wear. They 
are less hard than granite and wear more rapidly, but 
do not become so smooth and slippery, and commonly 
form a pavement that is more satisfactory from the 
point of view of the user. Sandstones differ very 
widely in character, their value depending chiefly upon 
the nature of the cementing material which holds them 



280 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

together. In order that a stone may wear well and 
evenly in a pavement it is desirable that it be fine- 
grained, dense and homogeneous, as well as cemented 
by a material which is not brittle and is nearly imper- 
vious to moisture. Those sandstones in which the 
cementing material is of an argillaceous or calcareous 
nature are apt to be perishable when exposed to the 
weather. The Medina sandstones of Western New 
York and Ohio have been quite extensively used for 
paving purposes and prove a very satisfactory material 
for such use. 

Limestone has not usually been successful in use for 
the construction of block pavements on account of its 
lack of durability against atmospheric influences. The 
action of frost commonly causes weakness and shiver- 
ing, which produces uneven and destructive wear under 
traffic. There are, however, as wide variations in the 
characteristics of limestones as in those of sandstones, 
and there may be possible exceptions to the rule that, 
in general, limestone is not a desirable material for 
block pavement. 

Art. 70. Cobblestone Pavements. 

Cobblestones have in the past been quite extensively 
used in the construction of street pavements, although 
at the present time they have been for the most part 
abandoned. They are not usually durable pavements 
as the stones are easily loosened from their positions, 
although the stones themselves may be practically 
indestructible and used again and again in reconstruct- 
ing the surface. 

Cobblestone pavements as commonly constructed 
are also objectionable because they are permeable to 



STONE-BLOCK PAVEMENTS. 28 1 

water and difficult to clean. They therefore collect, 
and become saturated with, the filth of the street 
and are very liable to injury from frost. They are 
also extremely rough and unsatisfactory in use for 
travel. 

For paving the side-gutters, where broken stone or 
sometimes where wood is used for the traveled portion 
of the street, cobblestones may often be convenient 
and useful, and form a cheap and satisfactory means 
of disposing of surface drainage. Such an arrange- 
ment is shown in Fig. 33 (p. 297). 

Cobblestones as used for pavements are usually 
rounded pebbles from 3 to 8 inches in diameter. They 
are set on end in a layer of sand or gravel, rammed into 
place until firmly held in position, and then covered 
with sand or fine gravel and left to the action of travel, 
which soon works the upper layer of sand into the 
interstices between the stones. 

Art. 71. Belgian Blocks. 

Belgian block is the name commonly applied to a 
pavement formed of nearly cubical blocks of hard rock. 
In the vicinity of New York this pavement has been 
largely used, the material being trap-rock from the 
valley of the lower Hudson. The blocks are usually 
from 5 to 7 inches upon the edges, with nearly parallel 
faces, and as commonly laid are placed upon a founda- 
tion layer of sand or gravel about 6 inches thick. This 
shape of block is objectionable on account of the width 
between joints being too great to afford good foothold 
to horses. The materials of which Belgian blocks have 
ordinarily been formed are very hard and (as already 
noted in Art. 69) wear smooth in service, becoming 



282 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

slipped and thus increasing the effect of the too wide 
block. It is also better to have the length of the 
blocks somewhat greater across the street and let them 
break joints in that direction in order that they may 
give greater resistance to displacement under passing 
wheel-loads. 

The older pavements of this character were usually 
placed upon a sand foundation. More recently this 
practice has, in the better class of work, been super- 
seded by a more solid construction, a concrete base 
being used. 

These pavements are now very little used, having 
given place to granite or sandstone blocks. 

Art. 72. Granite and Sandstone Blocks. 

For the construction of the better class of stone- 
block pavements, blocks of tough granite or sandstone 
are used, set, in the best work, upon a concrete base, 
although sometimes placed upon a foundation of sand 
or gravel. 

These pavements when well constructed are about 
the most satisfactory means yet devised for providing 
for very heavy traffic, as they present a maximum 
resistance to wear with a fairly good foothold for horses, 
and are much more agreeable in service than the 
old form of rough pavements. There is still much to 
be desired in the attainment of smoothness and ab- 
sence of noise, and, as a general thing, it may be said 
that pavements of this kind are desirable only where 
the weight of traffic is so great that the smoother pave- 
ments would not offer sufficient resistance to wear. 
Even in such cases it may frequently be questionable 
whether an additional expense for maintaining a pave- 



STONE-BLOCK PAVEMENTS. 2S3 

ment which would be more pleasant in use and less 
objectionable to occupants of adjoining premises would 
not be advisable from an economical as well as from 
an aesthetic point of view. 

Blocks for stone pavements, in the best work, are cut 
in the form of parallelopipeds, 9 to 12 inches long, 3 
inches wide, and 6 or 7 inches deep. The length should 
be sufficient to permit the blocks to break joints across 
the street. The width should be less than that of a 
horse's hoof in order that the joints in the direction of 
travel may be close enough together to prevent a horse 
from slipping in getting a foothold. The depth should 
be sufficient to give a bearing surface in the joints 
large enough to prevent the blocks from tipping when 
the load comes upon one end of them. 

Specifications for granite blocks in New York City 
in 1908 are as follows: 

"The blocks to be used shall be of a durable, sound 
and uniform quality of granite, each stone measuring 
not less than eight (8) inches, nor more than twelve (12) 
inches in length; not less than three and one-half (3^) 
nor more than four and one-half (4!) inches in width, 
and not less than seven (7) nor more than eight (8) 
inches in depth, and the stones shall be of the same 
quality as to hardness, color and grain. No outcrop, 
soft, brittle or laminated stone will be accepted. The 
blocks are to be rectangular on top and sides, uniform 
in thickness, to lay closely, and with fair and true 
surfaces, free from bunches. Over special construc- 
tions, the blocks may be of dimensions other than 
above specified when approved by the Engineer. The 
stone from each quarry shall be piled and laid separately 
in different sections of the work, and in no case shall the 
stones from different quarries be mixed. " 



284 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 73. Construction of Stone-block 
Pavements. 

Stone-block pavement for durable and effective 
service should be placed upon very firm foundations. 
Bases of concrete are usually employed and give the 
best results. These foundations are formed as described ♦ 
in Art. 47, and consist of a layer of concrete 4 to 8 
inches thick, 6 inches being the most common depth. 

In constructing the pavement, a cushion coat of sand, 
usually I to 2 inches thick, is spread upon the base of 
concrete for the purpose of allowing the bases of the 
paving blocks to be firmly bedded when the tops are 
brought to an even surface, the sand readily adjusting 
itself so as to fill all the spaces beneath the blocks and 
to offer a uniform resistance to downward motion in 
every part of the pavement, and in like manner trans- 
mitting the loads which come upon the pavement to 
the foundation so as to evenly distribute them over the 
surface of the concrete. The sand used for this pur- 
pose should be clean and dry, and all large particles 
sifted out, as they may prevent the blocks adjusting 
themselves properly. A thin layer of asphaltic cement 
is sometimes used in place of the sand with very good 
results. 

The blocks should be laid as close together as pos- 
sible in order to make the joints small. They are laid, 
like brick, with the longest dimension across the street, 
and arranged in courses transverse to the street, with 
the stone in consecutive courses breaking joints. 

After the blocks are placed they are well rammed to 
a firm unyielding bearing and an even surface. Stones 
that sink too low under the ramming must be taken 
out and raised by putting more sand underneath. 



STONE-BLOCK PAVEMENTS. 285 

As in the case of other block pavements, those of 
stone should be made as impervious to moisture as 
possible. The foundation should be kept dry, and 
moisture prevented from penetrating beneath the 
blocks where it has a tendency to cause unequal settle- 
ment under loads or disruptions under the action of 
frost. In the better class of work, therefore, the joints 
are filled with an impervious material which cements 
the blocks together. Asphalt or coal-tar paving cement 
is commonly employed for this purpose, as with brick 
and wood, and seems the most satisfactory in use, 
although hydraulic cement mortar is sometimes used. 
The coal-tar cement is commonly made by mixing 
coal-tar pitch with gas-tar and oil of creosote, a pro- 
portion sometimes employed being 100 pounds pitch, 
4 gallons tar, and I gallon creosote. 

The use of cement between the blocks binds them 
together and increases the strength of the pavement as 
well as the resistance of the blocks to being forced out 
of surface. It also deadens to some extent the noise 
from the passing of vehicles where asphaltic or coal-tar 
cement is used. 

A method commonly used for filling the joints is to 
first fill them about one third full of small gravel, then 
pour in the paving cement until it stands above the 
gravel; then another third full of gravel, more cement 
as before; then gravel to a little below the top, and the 
joint filled full of cement; after which a coating of 
fine gravel is distributed over the surface. 

Sometimes the joints are filled with gravel before the 
blocks are rammed to surface, and the paving cement 
afterward poured into the joints. This has the advan- 
tage of bringing the blocks to a very firm bearing, and 
secures complete filling of the joints. 



286 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Various modifications of the method above outlined 
are used in the principal cities for a pavement to with- 
stand heaviest traffic and secure a maximum of dura- 
bility; essentially it represents the best modern practice. 
The specifications used in New York City in 1908 
contain the following requirements: 

" 29. On the concrete foundation, as designated, shall 
be laid a bed of clean, coarse, dry sand to such depth 
(in no case less than one and a half [1 J] inches) as may 
be necessary to bring the surface of the pavement, 
when thoroughly rammed, to the proper grade. 

"On this sand bed, and to the grade and crown 
specified, shall be laid the stone blocks at right angles 
to the line of the street or at such angle as may be 
directed. Each course of blocks shall be laid straight 
and regularly, with the end joints by a lap of at least 
three (3) inches, and in no case shall stone of different 
width be laid in the same course except on curbs. All 
joints shall be close joints except that when gravel 
filling is used, the joints between courses shall be not 
more than three-quarters (f ) of an inch in width. 

"After the blocks are laid on a concrete foundation, 
they shall be covered with a clean, hard and dry gravel, 
which shall have been artificially heated and dried in 
proper appliances, placed in close proximity to the 
work, the gravel to be brushed in until all the joints are 
filled therewith to within three (3) inches of the top. 
The gravel must be washed white quartz and be entirely 
free from sand or dirt, and must have passed through 
a sieve of five-eighths (f ) inch mesh and been retained 
by a three-eighths (|) inch mesh. 

"The blocks must then be thoroughly rammed and 
the ramming repeated until they are brought to an 
unyielding bearing with a .uniform surface, true to the 



STONE-BLOCK PAVEMENTS. 287 

given grade and crown. No ramming shall be done 
within twenty (20) feet of the face of the work that is 
being laid. 

" The boiling paving cement, heated to a temperature 
of 300 F. and of the composition hereinbefore described, 
shall then be poured into the joints until the same are 
full, and remain full to the top of the gravel. Hot 
gravel shall then be poured along the joints until they 
are full flush with the top of the blocks, when they 
shall again be poured with the paving cement till all 
voids are completely filled." 

Art. 74. Stone Trackways. 

In some of the European cities, particularly in Italy, 
stone trackways are sometimes employed on streets of 
heavy traffic for the purpose of diminishing traction. 
These trackways are formed of smooth blocks of stone 




Fig. 27. 

4 to 6 feet long, 18 to 24 inches wide, and 6 to 8 inches 
deep, laid flat and end to end so as to form a smooth 
surface upon which wheels may move with the least 
possible resistance. Between the tracks, and usually 
the remainder of the street, is commonly paved with 
cobble. The method of construction is shown in Fig. 
27. The tracks drain to the middle, and the pavement 
between is made concave and provided with openings 
into the storm sewers for the escape of surface-water. 
The track and pavement are laid upon a layer of sand 
resting upon a broken-stone or gravel foundation. 



288 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Such trackways are quite durable under heavy traffic, 
and give light tractive resistance. They are not, how- 
ever, desirable on the streets of towns where smooth 
pavements might be used, and are too expensive for 
use on country roads. 

Steel trackways have frequently been proposed, and 
in a few instances have been tried, but have not been 
found successful and do not seem likely to become of 
any considerable importance. 



CHAPTER XI. 

CITY STREETS. 

Art. 75. Arrangement of City Streets. 

The location of streets should be planned with a 
view to giving direct and easy communication between 
all parts of a city. The arrangement should also be 
such as to permit the subdivision of the area traversed 
by them in such a manner as to give the maximum of 
efficiency for business or residential purposes. The 
most obvious and satisfactory method of accomplishing 
these purposes is usually by the use of the rectangular 
system, with occasional diagonal streets along lines 
likely to be in the direction of considerable travel. 

Streets so far as possible should be systematically 
arranged and continuous throughout the extent of the 
city, both to facilitate travel and to admit of their being 
so named, and numbered that the locality of a place 
of business or residence may at once be evident, from 
its address, to any one familiar with the general plan 
of the city. The rectangular system is desirable on 
this account, and also because it furnishes blocks of the 
best form for subdivision into building lots. 

The proper arrangement of streets will always neces- 
sarily depend in some measure upon the natural feat- 
ures of the locality, and any system of arrangement 
will be more or less modified by local topography. 
Where for topographic or aesthetic reasons it may be 
considered desirable to use curved lines for the streets, 

289 



290 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the continuity and uniformity of arrangement should 
be maintained as far as possible. The use of curves 
on residence streets may sometimes be advantageous 
in reducing gradients or in its effect upon adjoining 
property through avoiding heavy earthwork. Where 
a change in direction is necessary the use of a curve 
usually gives a better appearance than an abrupt bend, 
unless the change can be effected at the intersection of 
a cross-street. Care is required, however, to prevent 
the local introduction of curvature disarranging the 
general plans and producing the chaotic condition due 
to an irregular use of short streets. 

In laying out a rectangular system of streets the 
blocks ordinarily will preferably be long and narrow. 
The distance needed between streets in one direction 
is only that necessary to the proper depth of lots, while 
in the other direction the streets need only be close 
enough to provide convenient communication for the 
travel and traffic. A convenient method would be to 
lay out the main streets so as to form squares large 
enough to permit the introduction of an intermediate^ 
minor street through the blocks. These minor streets 
may then be introduced in the direction that seems 
advisable in each locality. Such an arrangement is 
shown in Fig. 2&. The diagonal streets cut more space 
from the blocks traversed by them, but give more 
frontage and property fronting them will usually have 
more value than other property in its vicinity. 

The proper location for diagonal streets intended as 
thoroughfares for traffic is naturally determined by the 
positions of the business centers or public buildings 
and parks, from which they may radiate in such manner 
as to bring the outlying portions of the city into the 
most direct communication /possible. 



CITY STREETS, 



29I 



A city cannot usually be laid out complete. Its for- 
mation is a matter of gradual growth and enlargement, 
and the end cannot be seen from the beginning. For 
this reason it is frequently necessary to undergo great 
expense in the larger cities in cutting new streets or in 
changing the positions or dimensions of existing old 
ones in built-up districts in order to relieve the 
crowded condition of the streets, which hampers busi- 
ness and renders travel difficult and unpleasant. Much 
of this difficulty might frequently be obviated if in 



BOM 



Fig. 28. 



growing towns and cities proper attention were given 
to the regulation of suburban development. Such 
development should be under municipal control so 
far as to require at least that each new subdivision 
which opens new streets should be made with a view 
to affording proper ways of communication between 
adjoining properties by making streets continuous. 
Where such regulation does not exist streets will be 
laid in any manner to best develop the particular prop- 
erty in which they are placed. 

A good example of the advantages of systematic and 
liberal plans in street arrangement, as well as of the 



292 A TEXT-BOOK ON ROADS AND PAVEMENTS. 




Fig. 39, 



CITY STREETS. 



293 



evils of unregulated extension, is given by the case of 
Washington, D. C. 

Fig. 29 shows a portion of the city of Washington 
illustrating its systematic arrangement. It consists of 
a rectangular system, together with two sets of diag- 
onal avenues, and open squares or circles at the inter- 
sections of the avenues. 

Fig. 30 shows a number of suburban subdivisions on 
the borders of the city of Washington, made previous 



Bsdjg&S, 



C5SO 



isaKFRRfl 



on 



nn 




mm 



Fig. 30. 

to the adoption of the law regulating them. In some 
cases the streets of adjoining subdivisions have no 
communication with each other, and the general ten- 
dency is toward a labyrinth of short streets. The law 
now requires that all street extension within the Dis- 
trict of Columbia shall conform to the general plan of 
the city of Washington; and under the operation of 
this law the lines of many of the city streets have been 
extended to all parts of the District, and all of the 
suburban development is being gradually brought with 



294 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the city into one harmonious whole, on the same gen- 
erous plan that exists within the city. The rectification 
of the irregular plats upon the borders of the city must, 
however, be a matter of heavy expense to the District. 

Art. 76. Width and Cross-section. 

The width of city streets is important both on 
account of its influence upon the ease with which 
traffic may be conducted, and because of its effect upon 
the health and comfort of the people, by determining 
the amount of light and air which may penetrate into 
thickly built-up districts. 

To properly accommodate the traffic of commercial 
thoroughfares in business districts of towns of consider- 
able size, it is desirable that a street should have a 
width of 100 to 160 feet, the whole of it to be used for 
roadway and sidewalks. Wide streets are especially 
needed where, as in the larger cities, they are bordered 
by high buildings or are to carry lines of street railway. 

Residence streets in a town of considerable size, 
where houses are set out to the property line and stand 
close together, should have a width of at least 80 to 
100 feet in order to look well and give plenty of light 
and air. 

The streets in nearly all large towns are laid out too 
narrow; they are crowded and dingy. The chief diffi- 
culty is that the future of a street is not usually fore- 
seen when it is located. Owners in subdividing prop- 
erty are only anxious to get as many lots as possible 
out of it, and there are usually no regulations looking 
to the future health and comfort of residents when the 
street shall be built upon. In the growth of a town the 
nature of localities changes; Residence streets become 



CITY STREETS. 295 

business streets, streets devoted to retail trade become 
wholesale streets, and mercantile districts are given up 
to manufacturing. If a city could be laid out com- 
plete from the beginning it would be comparatively 
easy to consider the requirements to be met and locate 
the streets accordingly. Under existing conditions this 
is not possible, but a more liberal policy in planning 
streets would usually be found of advantage in any 
growth that may ensue. There is also very frequently 
an immediate financial advantage in the enhancement 
of values due to wide streets. A lot 100 feet deep on 
a street 80 feet wide will nearly always be of greater 
value than if the same lot be no feet deep and the 
street only 60 feet in width. 

In Washington, D. C, which probably has the best 
general system of any American city, no new street can 
be located less than 90 feet in width, and avenues 
must be at least 120 feet wide. Intermediate streets, 
called places, 60 feet wide, are allowed within blocks, 
but full-width streets must be located not more than 
600 feet apart. The value of this liberal policy to the 
city of Washington is evident not only in the increased 
comfort of the people, but in its large growth as a 
residential city and the increased value of property 
in it. 

While it is advantageous to have the street wide be- 
tween building-lines, it is not necessary that the whole 
street width be used for pavements. The street pave- 
ment should be gauged in width by the immediate 
necessities of the traffic which is to pass over it. The 
pavement should be wide enough to easily accommo- 
date the traffic, but any unnecessary width is a tax 
upon the community in the construction and mainte- 
nance of more pavement than should be required, and 



296 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

perhaps diminishes the length of street which may be 
improved with available funds. Thus, for a residence 
street in general a width of 30 to 35 feet between 
curbs is usually ample, with a foot -walk upon each side 
5 to 10 feet wide. The remainder of the street width 
should be made into lawns upon each side, with tree 
spaces between the sidewalk and roadway. 

Fig. 31 shows in partial section the arrangement of a 
90-foot residence street for moderate traffic. For resi- 
dence streets of lesser importance, where the travel 
is light and the street is only required to furnish 
facilities to meet the needs of its immediate locality, a 
less width of pavement may often be advantageously 



- — m i = 

. . JJ.3V. -an..- 



W7777777777777777777770 



- - - 33 Fr. -»"• 3 •* - -8 Ft: « • L.AWN 17 FV. 

Fig. 31. 

used. A pavement 24 feet wide is sufficient to accom- 
modate a very considerable amount of light driving, 
and in many places, especially in the smaller towns 
where funds for effective improvement are obtained 
with difficulty, even less widths may be employed with 
the result of improving the streets both in appearance 
and usefulness. All that is really needed in such cases 
is room for teams to pass comfortably and to turn 
without difficulty. The narrowing of roadways on 
streets of light traffic to what is really necessary may 
often make possible improvements which will turn a 
broad sea of mud into a narrow, hard roadway and a 
grass-plat. Fig. S 2 shows the arrangement of a village 
street 50 feet wide for light service. 

In many cases for village streets, where the traffic is 
light and it is essential that Jfre cost of construction be 



CITY STREETS. 



297 



low, it may be good practice to construct the traveled 
portion of the roadway of macadam, or other pave- 
ment, and use cobble gutters at the sides without 




curbs. Fig. 33 shows a roadway 30 feet wide, with 
macadam middle and cobble gutters. In Saginaw, 
Mich., this method has been followed, using either 
macadam or wood blocks for the middle portion, and 
in the report of City Engineer Roberts for 1893 it is 
recommended as economical and efficient. 

The cross-section of streets must be arranged with 
reference to proper surface drainage. The street is 




Fig. 33. 

given a crown at the middle to throw the water into 
the gutters, and sidewalks usually have a sufficient in- 
clination toward the gutter to cause them to drain over 
the curb. The crown necessary to insure good drain- 
age in the roadway depends upon the nature of the 
covering, being less as the surface is more smooth and 
less permeable to water. For macadam roadways, it 
may vary from about fa to fa of the width of the 
roadway. For the various pavements, the required 
crown varies from about fa to T ^ ff of the width, accord- 
ing to the smoothness of the surface and the permea- 
bility of the construction. For brick, asphalt, or 
wood-block surfaces, a crown of from fa to T J 5 of 



298 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the width is commonly ample. Stone blocks may 
need slightly more; while, on streets of considerable 
longitudinal slope, the crown may be made somewhat 
lighter. 

The form of section is usually a convex curve, 
sometimes circular but more often parabolic, the para- 
bolic curve differing but slightly from the circular. 
This form is shown in Fig. 34. The distance of the 
_P c b A 

rcnIllluumiiiHiiiiiHiirtm 




Fig. 34. 

curved surface below the horizontal through the highest 
point is proportional to the square of the horizontal 
distance from the center. Thus, if the distance A — D 
be divided into 3 equal parts, the vertical distance from 
B to the curve is one -ninth and from C four-ninths of 
that at D. 

The street is usually made practically level across, 
the curbs and sidewalks at the two sides being given the 

7/f. I I I ' I ■ 1 1 ■ , ■ r — , — ■ J , rZty 

Fig. 35. 

same elevation. The parking at the sides may have a 
slope between the sidewalk and the building-line when 
it is necessary or advantageous. Sometimes, on streets 
along a slope, expense may be saved or adjoining 
property benefited by placing the sidewalk at a dif- 
ferent elevation from that of the street, as shown in Fig. 
5, or by placing one curb lower than the other and 
moving the crown of the road to one side, as shown in 
Fig. 35- 



CITY STREETS. 



299 



The surface drainage of alleys is secured either by 
forming the section as in a street, with a crown at the 
middle and gutters and curbs at the sides, or, as is com- 
monly preferable with narrow alleys, by placing the 
gutter at the middle and sloping the pavement from 
the sides to the center. Where the gutter is in the 
middle it is common to make the bottom of the gutter 
of a flagstone 15 to 18 inches wide. Fig. 36 shows a 




Fig. 36. 

center-drained alley with block-stone pavement upon 
sand foundation. 

The form shown in Fig. 36 is also usually employed 
where concrete pavement is used for alleys, as is quite 
common. This is desirable in many instances on ac- 
count of the good drainage afforded, and the resistance 
of the .material to dampness. 

Fig. 37 shows a side-drained cobble pavement for an 



Fig. 37. 

alley. These have been extensively used in the past, 
being usually placed upon sand foundation. They are 
gradually being replaced by brick or concrete pave- 
ments. 

Art. 77. Street Grades. 

The grades of city streets necessarily depend mainly 
upon the topography of the site. Wherever possible, 



300 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

it is desirable that grades be uniform between cross- 
streets. 

In establishing grades for new streets through unim- 
proved property, they may usually be laid with refer- 
ence only to obtaining the most desirable gradients for 
the street within a proper limit of cost. But where 
improvements have already been made, and located 
with reference to the natural surface of the ground, it 
is frequently a matter of extreme difficulty to give a 
desirable grade to the streets without injury to adjoin- 
ing properties. In such cases it becomes a question of 
how far individual interests shall be sacrificed to the 
general good. It may be said in this connection that 
adjustments to new grades are usually accomplished 
much more easily than would be anticipated, and when 
accomplished the possession of a desirable grade is 
of very considerable value to adjoining property. Too 
great timidity should not, therefore, be felt in regard 
to making necessary changes because of the fear of in- 
juring property in the locality. 

Where a grade if made continuous between inter- 
secting streets would be nearly level, it is frequently 
necessary to put a summit in the middle of the block 
and give a light gradient downward in each direction 
to the cross streets in order to provide for surface drain- 
age. The amount of slope necessary to provide for 
proper drainage depends upon the character of the sur- 
face and smoothness of the gutter. For a surface of earth 
or macadam the slope should not be less than about I 
in ioo, and for paved streets from I in 200 to 1 in 250. 

In some cases it may be possible to give sufficient 
slope to gutters to carry off the surface-water by mak- 
ing the gutter deeper at the ends than in the middle of 
the block without making a summit in the crown of 



CITY STREETS. 3OI 

the street. The curb in such case would be made 
level or of uniform gradient. 

It may frequently be necessary to consider the 
effect of grade in determining the character of pave- 
ment to be employed upon a street. Asphalt is com- 
monly limited to grades of 4 or 5 per cent, although 
some engineers use it on 6 or 7 per cent grades. Brick 
is commonly used on grades up to about 8 per cent, 
and in some places has given satisfactory service on 10 
per cent grades. Wide joints, about \ inch, are some- 
times used in brick pavements on steep streets, in order 
to afford a better foothold for horses. This, however, 
in other instances appears to be unnecessary, provided 
the pavement is kept clean and in good condition. 

Wood blocks may safely be used on grades of 5 or 
6 per cent, while smooth stone blocks are employed in 
about the same manner as bricks, being if anything a 
little more slippery than bricks. Stone blocks of some- 
what rough character are successfully used in some 
instances on grades of 12 or 13 per cent. 

In a report on the streets of Duluth in 1890, Messrs. 
Rudolph Hering and Andrew Rosewater recommend 
for steep streets, in addition to the above, that brick 
may be used in which the tops are rounded, and that 
wood blocks for such use have their upper edges cham- 
fered on each side, or if round blocks be used, around 
the blocks. Subsequent experience has, however, 
seemed to indicate that, except in extreme cases, such 
special construction is not necessary. 

On the streets too steep for smooth pavement it is not 
unusual to pave part of the street width with a smooth 
pavement, like asphalt, and the remainder with stone 
blocks or some rough pavement for use in slippery 
weather. 



302 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Art. 78. Street Intersections. 

At intersections the crown of the roadway pavement 
on each street should, if possible, be continuous to the 
center of intersection, in order to prevent vehicles on 
one street from being subjected to the jar incident to 
passing over the gutter of the other. Where a storm- 
sewer is available into which the water from the gut- 
ters on the upper side can be emptied this is a simple 
matter, but where such sewers do not exist it requires 
the adoption of some special means of draining the 
gutters on the upper side. This may sometimes be 
accomplished by a culvert across the street, the gutters 
being somewhat depressed at the corners to bring the 
channel sufficiently low. In other cases, where the 
slope is sufficient, it is more satisfactory to construct 
an underground pipe-drain from the upper corner to 
some point in the gutter below the crossing. 

Where the rate of grade is such that it is feasible, it 
is desirable that the grade of both streets should be 
brought to a level at intersections. The top of the curb 
at the four corners should be at the same elevation, thus 
permitting the continuation of the full section of each 
roadway until they intersect. It is also desirable that 
the sidewalks at the corners be level; that is, the points 
a a in Fig. 38 should all be placed at the same eleva- 
tion, which will make the entire street section, includ- 
ing sidewalks, horizontal across the direction of travel 
on each street. 

On very steep slopes it may not be possible to flatten 
out the grade to a level in crossing transverse streets, 
and in such cases the elevations require study, and need 
to be carefully worked out for each particular case. In 
the report of Messrs. Rudolph Hering and Andrew 



CITY STREETS. 



303 



Rosewater upon the streets of Duluth, it is recom- 
mended that in all cases the grade shall be reduced to 
3 per cent between the curb lines of cross streets, and 
the grade of the curb reduced in all cases to 8 per cent 
for the width of the sidewalks of intersecting streets. 
This is to be considered the maximum allowable rate 
of transverse grade, and only to be employed in case of 
necessity. If in Fig. 38 the arrow represents the direc- 
tion of steep slope, and the street transverse to that 
direction has a roadway 40 feet wide with sidewalks 



e 



a 



Fig. 38. 

10 feet wide, the above limits would permit the curb 
at c to be 1.2 feet lower than that at b, and admit of 
a fall of 0.8 foot in the curb line from a to b and from 
c to d. If both streets have the same grade and 
width the curb at the lowest corner would be 2.4 feet 
lower than at the highest corner. 

Sometimes, where the parallel streets in one direction 
follow the lines of greatest slope, and the cross streets 
are normal to them, the proper grades at intersections 
may be arranged by giving the streets along the slope 
a section similar to that shown in Fig. 32 throughout 
its length, thus permitting the street in the direction 



304 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of slope to continue its grade across the intersection 
without altering at that point the side slope of the 
cross street. 

For a case of maximum slope this would make the 
section of the roadway of the cross street a plane sur- 
face sloping uniformly from the upper to the lower 
curb, or in Fig. 35 it would transfer the street crown to 
the upper curb. 

Art. 79. Footways. 

Footways are not required to bear the heavy loads 
which come upon the roadway pavement, but in streets 
of considerable travel are subjected to a continual 
abrading action, and for good service are required to 
be of a material which will resist abrasion well, of so 
uniform a texture as to wear evenly, and not hard 
enough to become smooth and slippery in use. 

A good sidewalk should always present an even sur- 
face, and therefore requires a firm foundation to resist 
the displacement of the blocks of which it may be com- 
posed. It must also be durable under atmospheric 
changes, and of material that may be easily cleaned. 
The materials commonly employed are gravel, wood, 
brick, asphalt, stone, and concrete. 

Gravel walks are the cheapest of footways where 
suitable material is available. They are constructed in 
a manner similar to that used for gravel roadways, and 
require that the bed of the walk be well drained, and 
that it be well compacted by rolling or ramming before 
the walk is placed upon it. The best gravel walks are 
usually built upon a base of rough stone. This base 
may be 6 or 8 inches thick, and forms a solid founda 
tion upon which the graved surface may be placed and 



CITY STREETS. 30$ 

sustained against settling. Walks constructed in this 
manner are frequently used in city parks where the 
travel is considerable. On suburban roads gravel 
walks usually consist of a thin surface of gravel laid 
upon the earth-bed, and are replaced by some other 
surface when a more expensive construction can be 
afforded. Gutters are frequently necessary to protect 
the walk from the wash of surface-water, which other- 
wise very quickly destroys it. 

Wood is commonly used for walks in the form of 
planks which are laid on stringers, the planks being 
placed perpendicularly to the direction of travel. It is 
comparatively short-lived, and requires considerable 
expenditure for repairs, as the material is perishable 
and also wears rapidly. 

Brick footway pavements have been extensively used 
for many years, and form, when well constructed, a very 
durable and satisfactory sidewalk. As commonly con- 
structed they consist of ordinary hard-burned bricks 
laid flat upon a layer of sand over the earth-bed. For 
light travel, pavements so constructed may last well 
and give good service; but they are apt to soon become 
uneven through the sinking of the bricks because of in- 
sufficient foundation. 

In constructing such a pavement the sand layer 
should be well compacted by rolling or ramming be- 
fore setting the bricks, which should also be rammed 
to a firm and even bearing. To give satisfactory re- 
sults a foundation of sand and gravel or broken stone 
should be formed 8 to 10 inches in thickness. In 
Washington a layer of gravel 4 inches thick and well 
compacted is used, with a layer of sand of the same 
thickness upon it to receive the surface. In forming 
the pavements, the bricks are laid flat and as close as 



306 A TEXT-BOOK ON ROADS AND PAVEMENTS 

possible. The joints are filled with sand, usually by 
coating the surface with a layer of sand before ram- 
ming and after completion a second coating, which is 
allowed to remain a few days after admitting the 
travel to it. 

Care must be used in selecting brick for this purpose 
to get only hard-burned brick of uniform quality, 
in order that the resistance to wear may be even. 
The use of vitrified paving brick, as used for roadway 
pavement, would be of advantage on walks subjected 
to heavy wear. 

The use of a concrete foundation and setting the 
brick on edge and in mortar, after the manner of con- 
structing a roadway pavement, makes a very durable 
sidewalk under heavy travel. It is, however, some- 
what expensive, and usually a stone surface would be 
preferable where such expense is to be incurred. 

Footway pavements of a concrete in which coal-tar 
is the binding material have been widely used, but have 
not usually been satisfactory in use. As commonly 
constructed they wear rapidly and soften, becoming 
very disagreeable in hot weather. Some pavements 
of this character have, however, shown fairly good 
service. 

Numerous methods have been proposed and tried 
for the construction of tar footwalks, differing from 
each other in the materials mixed with the tar to form 
the concrete, and in the manipulation of the process. 
Ashes mixed with sand and gravel are usually em- 
ployed, and sometimes clinkers from an iron foundry. 
A somewhat successful pavement of this class has a 
small amount of Portland cement mixed with the ashes 
and sand used in forming the concrete before the addi- 
tion of the tar. *» 



CITY STREETS, 307 

Asphalt footway pavements are formed either of as- 
phalt blocks or of a surface of sheet asphalt. Where 
blocks are used they are laid in the same manner as 
brick upon a foundation of sand or gravel. The 
blocks, or tiles as they are commonly called, are usu- 
ally made flat, about 8 inches square and 2 to 2 J inches 
thick. They are laid with their edges either at right 
angles to the street line or at an angle of 45 with 
the street line — usually at right angles, on account 
of greater ease in laying. 

Sheet-asphalt footways are laid in the same manner 
as an asphalt street pavement, the pavement, however, 
being given a less thickness. In Washington, D. C, 
these pavements are made about 3 inches thick, and 
constructed upon a bituminous base. Material re- 
moved from street pavements in re-surfacing is used 
for forming the surface material of the footway. 

In Europe rock asphalt is frequently used for foot- 
ways, Asphalt mastic is commonly employed, mixed 
with sand or gravel to give a wearing surface. The in- 
gredients are heated together and applied hot to a 
broken-stone or concrete foundation. In Europe hy- 
draulic cement concrete is used for the base, as in the 
driveways. A layer of 3 or 4 inches of concrete is em- 
ployed, with a surface layer of rock asphalt or asphalt 
mastic and sand, i to J inch in thickness for ordinary 
work. 

Natural stone for footwalks is ordinarily used in the 
form of flagging. Where flagstones of proper size and 
good wearing qualities may be readily obtained, this 
kind of pavement, if well laid, makes a durable and 
satisfactory footwalk. Flagstones should be set upon 
a solid foundation and be* firmly bedded so as to 
preserve an even surface. They should not be laid, as 



308 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

is common in many places, directly upon an earth-bed 
but should have a cushion layer of sand or of some 
porous material to prevent unequal settling under the 
action of frost* 

CONCRETE SIDEWALKS. 

Concrete pavements, when well constructed of 
good materials, make the most satisfactory of foot- 
ways. They form an even surface, quite agreeable in 
service, and are durable and economical where exposed 
to considerable travel. 

In the construction of a concrete sidewalk a base 
of cinders is usually employed, supporting a la3^er of 
rather meager concrete and a thin surface layer of 
cement mortar. The cinders are commonly 4 to 8 
inches thick, 6 inches being ample for most walks, and 
4 inches being sufficient for walks in residence districts 
of small travel, where the soil is firm. Care should be 
taken to insure the proper drainage of the base, so 
that water may not remain in the soil immediately 
under the walk, or stand in the cinders. The cinders 
should be placed to proper depth and well Camped 
with the upper surface parallel to the finished top of 
the pavement. 

The concrete base is usually 3 or 4 inches thick, and 
sometimes on streets of heavy traffic it is made 5 inches. 
The wearing coat is from \ inch to I inch in thickness, 
depending upon the wear to which it is to be subjected. 
A concrete base 3 J inches thick, with a wearing sur- 
face J inch thick, makes a very satisfactory walk for 
residence streets carrying moderate travel. 

The composition of the concrete base must depend 
largely upon the materials available in the locality. 
Either gravel or broken stone may be used, with or 



CITY STREETS. 309 

without sand, according to the character of the 
materials. A mixture of one part Portland cement, 
three parts sand, and six parts broken stone is com- 
monly used. When good limestone is available, a 
mixture of one part Portland cement to four parts 
broken stone, without sand, is found very satisfactory, 
the stone being broken to pass a one inch screen and 
with only the fine dust removed. When sand or gravel 
is used, it is important that it be clean, as any dirt is 
likely to work to the surface in tamping and prevent the 
proper adhesion of the surface layer. For the same 
reason, the concrete must net be mixed too wet, and it 
should be well compacted by ramming. 

The wearing coat is composed of Portland cement 
mortar, one part cement to one or two parts sand or 
screenings. The amount of cement used should be 
sufficient to fill the voids in the sand but not greatly in 
excess, as the resistance to abrasion is lessened by 
excess of cement. The material for wearing coat should 
be either clean, hard sand, or screenings from the 
crushed stone. The screenings should have the very 
fine dust removed, and when from a good quality of 
rock are superior to most natural sands. The mortar 
is brought to a uniform surface by drawing a straight 
edge along the tops of the forms at the sides of the walk. 
The surface is then worked smooth and uniform with a 
float and finished with a plastering trowel. 

Joints should be left at intervals of 4 or 5 feet to 
prevent irregular cracks through contraction of the 
concrete. These joints need not all extend through 
the base of the walk, but at intervals of 3 or 4 joints 
one should extend through. The surface of a concrete 
walk should have a transverse slope of about J inch 
to I foot to provide for proper surface drainage. For 



310 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

residence streets of moderate travel a width of four to 
six feet is commonly required. Four feet is incon- 
veniently narrow unless the street is very little used, 
while six feet is sufficient for a very considerable 
amount of travel. 

• 

Art. 80. Curbs and Gutters. 

Curbs are usually set in the streets of towns at the 
sides of roadway pavements for the purpose of sus- 
taining and protecting the sidewalk or tree space, and 
of forming the side of the gutter. They are commonly 
formed of natural stone or concrete, but sometimes clay 
blocks are used. 

STONE CURBS. 

The curbs used in different places vary considerably 
in form and dimensions. Stone curbs vary from 4 to 
12. inches in width and from 8 to 24 inches in depth. 
They are usually employed from 3 to 6 feet in length 
and set with close joints. 

The depth must be sufficient to admit of their being 
firmly bedded, and to prevent overturning into the 
gutter. The front of the curb should be hammer- 
dressed to a depth greater than its exposure above the 
gutter, and the back deep enough to permit the side- 
walk pavement to fit close against it where the side- 
walk adjoins the curb. The ends of the blocks should 
also be dressed to the depth of exposure, and the part 
below the ground trimmed off so as to permit the 
dressed ends to come in contact when laid. 

Granite is usually considered the best material for 
curbs, although both sandstones and limestones are 
used in many places. In the vicinity of New York the 



CITY STREETS. 



3U 



North River bluestone has proved a good material for 
the purpose. 

There are various ways of setting the curb. The 
object should be to bed it firmly on a solid foundation. 





P 


W{< 










mm 








v*7*a'.i--'l7.' 




b^i 













Fig. 39. 

The best method is to place a bed of concrete under it. 
This construction is shown in Fig. 39, which repre- 
sents the method used in setting granite curb in Wash- 




Fig. 40. 

ington, D. C. The curb is held firmly in place by the 
concrete foundation, which joins it rigidly to the road- 
way pavement. 

Where the concrete foundation is not used under 



312 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the curb a deeper curbstone is necessary, usually from 
1 8 to 24 inches in good work. Curbs are very com- 
monly set in the natural ground, the pavement coming 
against it on one side; but it is usually found advan- 
tageous to lay them upon a bed of gravel or broken 
stone, with gravel filled in the trench about them. 
The ordinary method of setting curbs is shown in 
Fig. 40. 

The Washington specifications for ordinary work 
require that a bed of gravel 4 inches deep be used 
under the curb, and that the trench be filled with 
gravel placed in layers 3 or 4 inches deep, each layer 
being thoroughly rammed before adding the next. 

CONCRETE CURBS. 

Concrete curbs are extensively used, and their use is 
rapidly increasing, particularly in those sections where 
suitable natural stone does not occur. These curbs 
consist of concrete built in place in plank forms, 
extending continuously along the street, occasional 
joints being introduced to prevent irregular cracking. 
The concrete is laid and surfaced in the same manner 
as in sidewalk work, all exposed faces being surfaced 
with mortar. For curbs upon streets of light travel 
concrete mixed in the same proportions as for sidewalks 
gives good service; but where the use is more severe, a 
richer mixture will afford more strength, and about one 
part cement, two parts sand, and four of broken stone 
are frequently employed. 

The curb usually extends to the bottom of the base 
of the pavement, the concrete base joining the curb and 
holding it in place. For residence streets the curb is 
commonly 5 or 6 inches thick, while upon heavy traffic 



CITY STREETS. 313 

streets it may be made 8 or 10 inches thick. Where 
the traffic is very severe, concrete curbs are frequently 
reinforced, or faced, with steel at the edges for greater 
resistance to shocks. Several forms of patented rein- 
forcement are available for such use. 



BURNED CLAY CURBS. 

Burned clay curbs are sometimes employed in small 
towns where brick pavements are used. These are 
made in such small sizes and short lengths that they 
are difficult to set to good line and are easily displaced. 
They have not in general proved satisfactory. 

Curbs at street corners and driveways are commonly 
laid upon curves. On ordinary residence streets curves 
of 4 to 6 feet radius are usually employed, while 
upon wide streets with considerable traffic curves of 
8 to 12 feet radius are desirable. These are easily set 
for concrete curbing by having forms to fit the whole 
curve. For curves of 3 or 4 feet radius stone curbing 
may be cut in two pieces for a right-angled turn. 
With curves of larger radius more pieces must be used 
and the cutting and setting becomes more expensive. 

GUTTERS. 

Gutters are commonly formed of the same material 
as the roadway pavement, which is simply extended 
to the curb. 

In streets paved with brick or granite blocks the 
gutter blocks are sometimes turned lengthwise of the 
street, as shown in Fig. 22, for the purpose of facilitat- 
ing the flow of water in the gutter. As already pointed 
out, however, this has the effect of making a continuous 



314 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

joint between the pavement and gutter, and its utility 
seems doubtful. 

For streets paved with broken stone it is common to 
employ stone gutters, formed of cobblestones, of narrow 
flags laid lengthwise of the gutter, or sometimes of rec- 
tangular blocks. Such construction is shown in Fig. 40. 
On streets paved with wood these gutters may also be 
frequently employed with advantage, especially where 
for any reason the gutter is likely to be kept damp. 
In forming a cobble gutter the stones are usually set 
upon a layer of sand or gravel after the manner of 
forming a cobble pavement. They should be firmly 
bedded and form an even surface. 

Cobble gutters are often used on village streets 
where no curbs are set, and in such locations, where 
but slight expense is admissible, they are quite satis- 
factory if properly constructed. This method of con- 
struction is illustrated in Fig. 33. 

Sometimes in work of this kind a flagstone is used 
for the bottom of the gutter and the sides are formed of 
cobble. This is preferable as affording a more free 
channel for the flow of the surface drainage. 

To obtain satisfactory results it is always necessary 
that the foundation be of sufficient depth and well 
compacted in order to prevent the surface becoming 
uneven by the stones being forced downward into the 
road-bed in wet weather or through the action of frost. 
A layer of 6 to 10 inches of gravel or sand is usually 
required. 

Where flagstones are used to form the gutter, they 
should be 3 or 4 inches thick, 10 to 15 inches wide, as 
may be required, and about 3 feet long. Care is 
required in laying that they may have an even bed and 
be well supported by the foundation. 



CITY STREETS 315 

Gutters of bricks, or of stone blocks, are often used for 
streets upon which the roadway pavement is asphalt, 
on account of the liability of the asphalt being injured 
by dampness. In this case the gutter is constructed 
by setting the bricks or blocks with their greatest 
length along the street. They are placed upon a bed 
of concrete, the same as is used for the foundation 
under the asphalt surface, and the joints are filled 
with hydraulic cement mortar, as in constructing brick 
pavement. 

CONCRETE GUTTERS. 

Concrete gutters are quite commonly used on streets 
paved with macadam, and sometimes at the sides 
of asphalt streets. These are sometimes flat curved 
gutters, similar in form to the cobble gutter shown in 
Fig. 33, but more commonly they are used with con- 
crete curbs as combined curb and gutter. These 
consist simply of the concrete curb with a concrete 
gutter 18 to 30 inches wide attached and built together 
in one piece. This is usually placed, like a sidewalk, 
upon a layer of cinders or gravel, and is constructed in 
the same manner, the gutter, upon streets of moderate 
traffic, being usually about 5 or 6 inches thick. 

Where the street pavement is carefully laid flush 
with the gutter, this makes a very satisfactory gutter. 
Upon macadam streets considerable trouble is some- 
times experienced in keeping the surface of the macadam 
up to the level of the gutter, and in many instances, 
unless considerable care is taken both in construction 
and maintenance, a second gutter forms in the surface 
of the macadam next to the concrete gutter. This is 
due to the difficulty of properly compacting the mac- 
adam next to the gutter, as well as to the greater wear 



316 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of the macadam and the effect of rain in washing it. 
To secure good results it is essential that the macadam 
be brought flush with the concrete gutter so that the 
water may readily pass into the gutter, and that it be 
well compacted so as to prevent subsequent settlement. 

Art. 8i. Crossings. 

On streets paved with a smooth hard surface which 
is easily cleaned, such as brick or asphalt, special foot- 
way crossings are not usually required or desirable, 
unless the foot travel be very considerable. On other 
pavements, however, which are apt to be rough to 
walk upon or muddy in bad weather, as upon stone, 
or macadam, footways of flagstones, brick, or concrete 
are commonly provided. 

Stone crossings consist of flagstones about 10 or 12 
inches wide laid in rows across the street, the rows 
being 6 or 8 inches apart and paved between with stone 
blocks set in the ordinary manner. The crossing- 
stones are 3 or 4 feet long, and at least 6 inches thick 
in order that they may not be broken by the traffic. 
They should be laid with close joints and firmly bedded 
upon the foundation. 

Brick crossings are usually constructed in the same 
manner as brick street pavements, being laid upon 
concrete base and having joints filled with cement 
mortar. They should be slightly crowned, so as to 
raise the crossing a little above the general level of the 
street and facilitate keeping them clean. These cross- 
ings are sometimes laid as double layer brick pavements 
with sand filled joints, but in general the better grade 
of construction is but slightly more expensive and is 
much more durable in use. 



CITY STREETS. 317 

Concrete street crossings are placed in the same 
manner as concrete sidewalks. They should, like brick 
crossings, have a crown to aid in keeping them clean. 
Crossings, and sidewalks across alley openings or drive- 
ways, need to be somewhat heavier than ordinary 
sidewalks and are usually about 6 inches thick. It is 
common to cut longitudinal V-shaped grooves, about 
\ inch to I inch wide, \ to \ inch deep, and 4 inches 
apart, in the surface of the walk to afford a foothold to 
horses in crossing it. These grooves may readily be 
formed by use of the tool used in finishing joints, and 
are of material benefit in preventing the slipping of 
horses. 

At street intersections where the number of pedes- 
trians is large it is desirable that the crossing be carried 
across on the level of the top of the curb without 
leaving a step at the gutter crossing. This may be 
accomplished by bridging over the gutter with a flag- 
stone or iron plate, or by placing the outlets for surface 
drainage a few feet back from the corner and eliminating 
the gutter at the corner. 

Art. 82. Street-railway Track. 

Track for street railways upon paved streets should 
be constructed with a view to offering as little obstruc- 
tion to ordinary street traffic as possible, while per- 
mitting the ready operation of the railway. These 
two points are apt to conflict, as the interest of the 
railway company in the construction of track is rarely 
identical with that of the public use of the street. 

Any street-car track is objectionable on a paved 
street, both on account of the increased wear caused 
to the pavement, and because it forms an obstruction 



318 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

to the ordinary traffic of the street. It is, however, 
a necessary evil, being required for the convenience 
of the public, and its detrimental effects may often be 
greatly lessened by proper attention to the methods 
of construction employed. On smooth pavements 
properly constructed track should offer no obstruction 
to vehicles crossing it, and afford no channels in which 
the wheels of vehicles may run and which prevent 
wheels readily leaving the track. 

This requires that the surface of the pavement be 
flush with the top of the rail, and that it be laid in 
close contact with the rail. 

It is also important that the method of construction 
used in both track and pavement be firm and substan- 
tial to prevent unevenness due to the yielding of the 
track or settlement of the pavement. 

Construction of Track. Methods of construction 
used for street railway tracks are extremely various 
and opinions differ widely concerning them. When 
the traffic of the railway and street is light it is gen- 
erally conceded that the most economical method is 
that of placing the rails directly upon wooden cross- 
ties, as in the construction of steam roads. Where, 
however, the traffic is heavy the difficulty and ex- 
pense of making repairs becomes great, and the rail- 
way companies commonly recognize the advantage of 
solid and permanent construction. Several methods 
have therefore been devised for securing firm support 
to the rails. 

Fig. 41 shows the ordinary method of construction 
where a concrete base is employed for the pavement 
and the tie is embedded in the concrete. In this con- 
struction the track is surfaced up by ballasting in the 
usual manner under the ties with gravel or broken 



CITY STREETS. 319 

stone, after which the concrete base is filled in between 
and perhaps over the ties. The depth of rail is some- 
times made the same as the thickness of the upper 
layers of pavement, thus bringing the top of the tie 




Fig. 41. 

even with the surface of the concrete. Thus a six- 
inch rail may be used with a brick pavement having 
a two-inch sand cushion as shown in Fig. 42. If the 
depth of rail be less than this, stringers, as in Fig. 43, 




Fig. 42. 

or chairs, as in Fig. 44, are necessary to raise the rails 
to the level of the paving surface. When stringers 
are employed they are usually connected by cast-iron 
braces to the cross-ties, and are also bedded and held 
in place by the concrete base of the pavement. The 
ties in such case are usually below the concrete. To 
secure greater stability when the rails are supported 



320 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

by cross-ties a bed of concrete is sometimes placed 
under each tie and the track is tamped in concrete. 
This is shown in Figs. 42 and 44. In such construc- 
tion it is usual to make a trench under the tie, fill this 




Fig. 43. 

with concrete and tamp the tie with concrete, after- 
ward placing the concrete base for the pavement be- 
tween the ties. 

On important lines in streets of heavy traffic re- 
pairs to track are often both difficult and expensive, 




Fig. 44. 

and very rigid and substantial construction is essential 
to an economical operation of the railway. To secure 
such construction the wooden ties are sometimes dis- 
pensed with and the rails placed directly upon the 
concrete. Several methods of construction of this 
character have been employed. Fig. 45 shows the 
simplest form, where the rails are placed directly upon 



CITY STREETS. 



321 



the concrete base of the pavement and spaced by iron 
tie-rods at intervals of six or eight feet. The con- 
crete in this construction is usually made extra heavy 
in order to adequately support the rails and maintain 
them at the level of the pavement. 

A more economical method of securing permanent 




Fig."45- 

construction is by the use of a concrete beam or 
stringer under the rail. This method of construction 
is illustrated in Fig. 46. The concrete stringers are 
usually made of Portland-cement concrete from 9 to 




Fig. 46. 

12 inches in depth and 12 to 18 inches in width The 
rails are commonly held in place by iron ties, to which 
the base of the rail is bolted, as shown in figure. Fre- 
quently light angle-bars are used for ties, but various 
other sections have also been employed for which 
special advantages are claimed. Spacing rods between 
the webs of the rails may also be employed as shown 
in Fig. 45, but these rods are objectionable in a block 
pavement on account of the difficulty of paving be- 



322 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

tween them. The ties are usually spaced about ten 
feet apart. 

In some instances, where concrete beams are used 
under the rails, ties are omitted altogether and the 
base of the rail is spiked directly to the concrete or 
bolted through the concrete beam to plates below. 
This latter method has been carried out at Rochester, 
N. Y., with entire success, no difficulty being experi- 
enced in holding the rails in position. In construct- 
ing such track the rails are usually laid on temporary 
wooden ties spaced ten or twelve feet apart and 
brought to line and grade, after which the concrete 
beams are placed and the wooden ties removed. 

Form for Rails. The rails in common use for 
street-railway track are divided into two general 
classes: tee rails, as commonly used on steam roads, 
and girder rails, in which the head is so formed as to 
afford a channel for the flanges of the wheels and ad- 
mit of the pavement being laid close against the rail 
on both sides. 

Tee rails differ considerably in their details and 
weights and are often modified for street service by 
making them of greater depth than is usual for steam- 
road service. These rails are shown in Figs. 42 and 
43. The upper surface varies from 2 to 3 inches in 
width and is usually made convex, the section being 
frequently circular, of radius 8 to 20 inches. As used 
for street railways, these rails vary from 4 to 7 inches 
in height. In using the smaller depths it is necessary, 
except for very thin paving surfaces, that the rails be 
supported on chairs or stringers to give room for pav- 
ing over the cross-ties, and deeper sections are there- 
fore more commonly used. The six-inch depth is fre- 
quently employed and is sufficient with an asphalt or 



CITY STREETS. 323 

brick pavement, the ties, if used, being embedded in 
the concrete foundation. 

The disadvantage of the tee rail consists in the fact 
that the pavement cannot come against the rail on the 
inside of the track, as it has no groove for the wheel- 
flange. The pavement must therefore either be low- 
ered under the rail-flange or a groove be left between 
the head of the rail and the pavement. The first 
method, shown in Fig. 42, is ordinarily the best con- 
struction, as the pavement is set firmly against the rails 
and there are no exposed edges to cause rapid wear, but 
it is objectionable on account of the impact of wheels 
crossing in dropping from the rail, and because it tends 
to hold the wheels of vehicles in the track. The 
second method is accomplished by using a thin block 
or a filling of concrete under the head of the rail and 
paving against this filling, as is usual when stone-block 
pavement is employed between the rails, or when a 
toothing of stone blocks or bricks is employed with 
an asphalt pavement. For brick pavements special 
bricks are sometimes molded to fit against the rails, 
leaving a groove for the wheel-flanges, as shown in 
Fig. 43. Difficulty has sometimes been met in the 
use of these bricks on account of their tendency to tilt 
when the car-wheel flanges press down any dirt or 
small gravel which may fall into the groove, unless 
they are very firmly bedded next the rail. Tee-rail 
construction is very commonly preferred by railway 
companies, as giving a better road for operation. It 
affords cheap construction, has little tendency to be- 
come clogged with dirt, and will usually be avoided 
by the ordinary traffic of the street, not affording good 
channels for the wheels of vehicles. 

Girder rails are divided as to form of head into 



324 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



center-bearing, side-bearing, and grooved. They vary, 
as commonly used, from 6 to 9 inches in height, and 
each type is subject to several variations in form. 

The center-bearing rail is shown in Fig. 47. It is 
the most objectionable of any of the forms in use, 
there being two channels, one on each side of the 
head, thus offering a double obstruction 
to traffic and causing greatly increased 
wear to the pavement. It is of advan- 
tage to the traffic of the railway because 
it does not retain dirt, and where streets 
are not kept in good condition cleanses 
itself, which is particularly important 
IG * 4 ?* on electric roads in which the rail is used 

as a current conductor. Its objectionable features, 
however, prevent its use in most places. 

Side-bearing rails are shown in Figs. 44, 48, and 49. 
They are probably more commonly used than any 





Fig. 48. 

other type of girder rail. The tram is from 2 to 3 
inches wide and offers a smooth track for the wheels 
of vehicles, but it is difficult for a wheel to leave it 
and is extremely hard on the street traffic. 

Pavements may be laid against the side-bearing rail 
as shown in Fig. 44, in which the surface of the pave; 
ment is at the same level inside as outside the track; 



CITY STREETS. 325 

or, as shown in Fig. 48, in which the pavement inside 
the track is brought even with the top of the tram of 
the rail. The first method leaves an exposed edge 
of the paving surface, which is commonly subject to 
rapid wear, while the width of tram is sufficient to per- 
mit the wheels of vehicles to run in the grooves and to 
leave the track with difficulty. 

Grooved rails are shown in Figs. 41, 45, 46, 50, and 
51. There are many variations in the form of groove 
and lip designed to meet varying conditions of use. 
The full-groove rail, shown in Fig. 41, has a groove in 
the head usually from an inch to an inch and a quarter 
in width; and when the pavement is made flush with 
the top of the rail it presents no obstruction to traffic 
of the street, and as the groove is too narrow to admit 
the wheels of vehicles it forms the most desirable track 
for use with smooth pavements. It can only, however, 
be used where pavements are kept clean and in good 
condition, as the groove is otherwise easily clogged with 
dirt, rendering the operation of the railway difficult 
and expensive. This disadvantage is greater in cold 
climates where snow and ice are common during 
winter. 

For the purpose of lessening the clogging of the 
groove, the form of the grooved rail is sometimes 
modified by sloping the lip and widening the groove 
at the top, as shown in Fig. 46 or, as shown in Fig. 50, 
by making the lip of a less height than the head of the 
rail, thus allowing the wheel-flange to clear the groove 
of dirt in passing. This latter form, however, has 
the effect of forming a track which retains the wheels of 
vehicles, as will any difference of elevation between the 
head of the rail and the pavement between the rails. 

In Fig. 51 is shown a grooved rail with an exten- 



326 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

sion of the lip intended to form a track for wheels of 
vehicles with a view to reducing the wear of the pave- 
ment which commonly takes place immediately inside 
the rails. When this lip is below the level of the rail- 
head it is subject to the same objection as the side- 
bearing rail of forming a track which it is difficult 
for wheels to leave. 

For paved streets, where the pavement is well kept, 
the grooved rail seems to be superior to any other, 
and is often required by municipal authorities, par- 




Fig. 49. 



Fig. 50. 



Fig. 51. 



ticularly in the larger cities. For unimproved streets 
or on macadam or earth roads the tee rail is usually 
considered preferable, and may usually be employed 
with no more injury to the street traffic than any of 
the others, while possessing the advantage of economy 
both in cost and operation to the railway. 

Joints and Fastenings. The solid construction of 
track is a matter of importance upon paved streets, 
because of the difficulty and expense of getting at the 
track to make repairs, as well as because of the dis- 
turbance to traffic when the pavement must be removed 



CITY STREETS. 32/ 

for this purpose. The rail-joints and tie-connections 
are therefore matters requiring particular attention. 
Where no chairs are used, the use of tie-plates to form 
a bearing for the rail upon the tie, and to hold it 
securely in place, is to be recommended, and will 
greatly aid in forming a rigid track. There are a 
number of forms in use which give good results. They 
should be arranged to clamp the rail firmly and present 
a good bearing upon the tie. When chairs are used, 
they, like the tie-plates, should clamp the rail firmly 
and give good bearing surface. They should also be 
well braced for stiffness against lateral bending. 

Joints, in the case of track formed of rails laid directly 
upon the ties, or upon wooden stringers, are usually 
made by placing a plate or channel-bar upon each side 
of the web of the rail-ends to be joined and bolting 
through. The use of slightly curved channel-bars 
fitting against the flanges of the rail, as shown 
in Figs. 49 and 51, seems to give good results, the 
spring in the channels serving to prevent the loosening 
of the bolts. This is the most common method of 
making joints. Fig. 50 shows a pair of ribbed-joint 
plates as used for high rails, the center bearing serving 
to prevent the buckling of the plates or the bending 
of the rail at the ends. 

For track in pavements the rails may be laid to 
close joints, no allowance being necessary for change 
of temperature when the rail is fully bedded in the 
pavement. 

A number of modifications of the above joints have 
been devised, some of them passing under the base of 
the rail and supporting it on the tie. Electrically 
welded or cast joints are also sometimes employed, 
consisting in welding a bar of steel on each side of the 



328 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

end of the rail, or in casting an iron block about the 
ends to be joined, the casting being joined by means 
of the holes through the web of the rails. 

Where chairs are employed to- raise the rails above 
the ties, joints are frequently most satisfactorily made 
upon long chairs or bridges reaching across the space 
between two ties and forming a firm bearing for the 
ends of the rails. 

In order to facilitate keeping the joints tight and 
enable the bolts at the rail-ends to be screwed up 
without taking up the pavement, joint -boxes are 
sometimes employed. These consist of openings with 
removable covers, giving access to the bolts at the 
ends of the rails. 

On curves, guard-rails are commonly employed. 
Where tee rails are employed the guard is usually a 
second rail placed on the inside of the main rail, leaving 
only room for the wheel-flanges. In some instances, 
however, the guard is formed by bolting a flange to 
the main rail. For girder rails the guard is usually 
formed by the use of a rail in which the groove is 
wider and the lip heavier than common, and sometimes 
the lip extends somewhat above the head of the rail. 
Any difference of elevation of that kind is objection- 
able as producing unevenness in the pavement, but is 
frequently used as essential to the proper operation of 
the cars upon the curves. 

Pavement in Car Tracks. The wear of a pavement 
is usually considerably increased by railway tracks 
upon the street. The extent of this wear depends 
upon the nature of the paving surface as well as upon 
the construction of the track. It is mainly the differ- 
ence in resistance to abrasive wear between the rails 
and the paving surface which causes uneven and more 



CITY STREETS. 329 

rapid wear of the pavement in vicinity of the track. 
A broken-stone surface, on account of its rapid wear, 
is particularly objectionable along a line of track, and 
is very difficult to keep in proper surface. 

In case of narrow streets or rough side-pave- 
ments the use of the track for hauling heavy loads 
causes the cutting of the pavement upon the outside 
of the track, due to the gauge of trucks being greater 
than that of the track. This is especially the case 
where, owing to the use of side-bearing or center- 
bearing rails, the flange -grooves are wide enough to 
permit the wheels of trucks to enter them. 

Where tracks follow country roads it is usually 
desirable, if possible, to place the track at one side 
and leave the center of the street free for the use of 
the ordinary traffic. When a broken-stone or gravel 
surface is employed it is common to lay planks on 
each side of the rail and bring the pavement against 
the planks, which materially lessens the obstruction 
offered to travel by the rails, as well as the difficulty 
of keeping the pavement in surface. 

The methods of placing pavements in tracks 
depend upon the shape of the rail-heads and have 
already been discussed. Under heavy traffic when 
asphalt street surface is employed it is quite common 
to pave between the rails with stone or brick, and 
often to put a toothing of the same material outside 
the rails adjoining the asphalt. This serves to prevent 
the cutting of the asphalt along the rails. Sometimes 
when stone blocks are used in track the concrete base 
is omitted and the blocks are set on a gravel or broken- 
stone base. When such construction is employed the 
track should be very carefully ballasted and brought 
to an even bearing. There is always a tendency for 



330 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the track to work loose from the pavement and get 
out of surface, and under heavy traffic very firm con- 
struction is necessary to counteract this tendency. 

Art. 83. Trees for Streets. 

It is always desirable, wherever possible, to have 
streets, at least those devoted to residential purposes, 
lined with rows of trees upon each side, both for the 
purpose of giving shade and to add to the beauty of 
appearance of the street. 

The most satisf acto^ way of arranging trees is usually 
to have a tree space between the sidewalk and the curb 
in which the trees are planted in a straight line along 
the street. Sometimes in very wide streets a tree 
space or parking is arranged in the middle of the street 
with a driveway on each side. Trees should be spaced 
in the rows at such distances as will permit each tree 
when fully grown to spread to its full natural dimen- 
sions, which usually requires, for trees ordinarily em- 
ployed, from 25 to 40 feet. 

The selection of the variety of trees to be used for 
this purpose must of course depend upon climatic 
and local conditions. Those which rapidly attain their 
full size are usually to be preferred. They should 
have a graceful form and make a good shade, but the 
foliage should not be too dense. Evergreens are not 
generally desirable for this purpose. Where there is 
plenty of room for their development the large-grow- 
mg varieties with light foliage are handsome and desir- 
able. The size, however, must be suited to the space, 
and upon narrow streets, or where the trees are to be 
close to the buildings, they must be of small growth. 
The ease with which the tree may be grown and its 



CITY STREETS. 331 

liability to disease or to be affected by the contamina- 
tions of a city atmosphere must be considered, as the 
conditions under which street trees must be grown are 
not usually favorable to their best development. 

It is desirable, especially in cities of considerable 
size, that the planting and care of trees be under con- 
trol of the municipal authorities. Trees may then be 
set with a view to the best general effect upon the 
street as a whole; the selection and planting of the 
trees may be properly done, and the trees after plant- 
ing may be systematically cared for. 

Art. 84. Selection of Pavements. 

The selection of the best pavement for use in any 
given instance involves a study of the characteristics 
of each material as to its fitness for the particular 
service required, its suitability for meeting the local 
conditions under which it is to be used, and its probable 
cost. Local conditions must be taken into account, 
and it is not possible to lay down any fixed rules for 
universal application. The availability of materials 
in the locality, and relative costs which vary with local 
conditions, are frequently determining factors in the 
choice of pavements. 

A good pavement should present a smooth, hard, and 
impervious surface, which may be easily cleaned and 
offers small resistance to traction. The comfort, con- 
venience, and health of people using the street and of 
residents of the locality may be largely affected by the 
character of a street, and should be the first considera- 
tion in deciding upon an improvement. 



332 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

HEALTHFULNESS. 

The effect of a pavement upon the health of the 
residents of its locality will be affected by the tendency 
of the materials composing it to decay, by its permea- 
bility, and by its degree of freedom from noise and 
dust. 

The permeability of a road surface is important on 
account of the tendency of surface water and refuse 
matter to penetrate and saturate it, and thus cause it 
to become dangerous to health. A continuous sheet 
pavement is the most desirable in this particular, and 
a block pavement with open joints the least so. When, 
however, the joints of a block pavement are properly 
cemented, the pavement may be made nearly imper- 
vious, and any of the pavements in common use, when 
well constructed, are practically impervious to water. 

Noiselessness. The noise made by traffic upon a 
pavement is important not only because of its effect 
upon the comfort of the people using it Or living 
adjacent to it, but also because to it are frequently 
attributed many nervous disorders to which people 
in some cities are subject. 

Stone-block pavements are the most objectionable 
in this particular, causing a continual roar, due both 
to the rumbling of wheels over them and the blows of 
the horses' feet upon them. Upon asphalt the noise is 
only that due to the horses' feet, giving a sharp, 
clicking sound. Upon wood the horses produce no 
appreciable sound; but wheels give a dull rumble, 
generally considered the least objectionable of any of 
the noises made by the more common pavements. 
The noise of wood pavements is diminished by mak- 
ing the joints between -blocks small, and a well con- 



CITY STREETS. 333 

structed wood-block pavement is usually the least 
noisy of the pavements in common use. The noise 
made by traffic upon a brick pavement varies with 
the method of construction. The clicking sound 
made by horses is less than on asphalt, but the rumble 
of vehicles is greater, the rumble being usually more 
objectionable with hydraulic cement than with bitu- 
minous or sand-filled joints, although when proper 
expansion joints are used with cement joints the noise 
is not excessive. 

Broken-stone roads are less noisy than any of the 
harder pavements excepting wood blocks, while earth 
roads are the most desirable on this account when in 
smooth condition. 

Freedom from Dust. The dust arising from a pave- 
ment is objectionable on the score of health as well 
as of comfort. For the most part the dust found upon 
city pavements is produced from dirt carried there 
from the outside. To eliminate this it is necessary to 
keep the pavement clean, and perhaps to sprinkle it. 
All pavements produce more or less dust, even when 
kept thoroughly cleaned. Stone, brick, and asphalt 
surfaces all give off a small amount of very fine dust, 
which rises in the wind unless the surface is kept 
sprinkled. Wood-block surfaces are less objectionable 
on this account. Broken-stone roads wear rapidly 
and make dust freely in dry weather, unless kept 
sprinkled or treated with oil or tar (see Art. 41). 

safety. 

The safety of a road surface depends upon the foot- 
hold afforded by it to horses under normal conditions, 
and also upon the degree of slipperiness that it may 



334 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

take in wet weather, or under the influence of ice and 
snow in winter. 

A dry earth road in good condition gives the best 
and surest foothold, with broken-stone and gravel 
roads nearly as good. 

The relative safety of the various pavements used in 
city streets is a matter upon which there is consider- 
able difference of opinion amongst authorities. Local 
conditions affect the pavement in this regard to an im- 
portant degree. The dampness of the climate, the 
shade from buildings, the cleanliness of the streets, 
and the prevalence of snow and ice in winter are all 
important. 

Statistics upon the question of relative safety of 
wood, asphalt, and granite have been collected by 
Captain Greene in this country and by Colonel 
Haywood in London, the attempt being made to deter- 
mine the number of miles traveled by horses upon each 
kind of pavement to each accident due to slipperiness. 

The results of Colonel Haywood seem to show that 
of the three, wood is the safest and granite the most 
dangerous, while the results of Captain Greene show 
asphalt to be the best and wood the worst in this 
particular. 

Colonel Haywood's observations were all taken on 
London streets, and are as follows: 





Miles Traveled to Each Fall on — 




Granite. 


Asphalt. 


Wood. 


In dry weather 


78 
168 

43 2 
132 


223 

125 
192 

191 


646 


In damp weather 


193 

537 
330 


In wet weather 


All observations 





CITY STREETS. 335 

The observations were made when dry weather 
prevailed, and therefore are somewhat unfavorable to 
granite, which is safest when wet. 

Captain Greene's observations were made in several 
American cities, and showed the distance traveled to 
each fall tb be, on granite 413 miles, on asphalt 583 
miles, and on wood 272 miles. The observations on 
wood in this series were too few to give a reliable in- 
dication, and it is to be observed with regard to all of 
them that slipperiness is largely affected by the con- 
dition in which the surface is maintained, and it is 
therefore difficult to draw any general conclusions 
which would fit all cases. 

All hard pavements are slippery when muddy and 
wet, and cleanliness is the necessary condition of 
safety. 

Wood and asphalt, if clean, are least slippery when 
dry and most so when simply damp. Granite, after 
the surface becomes worn and polished, is most slip- 
pery when dry and least so when wet. 

Under a light fall of snow both wood and asphalt 
become very slippery, and in freezing weather wood 
sometimes becomes slippery through the freezing of 
the moisture retained by it. 

No statistics are available as to the safety of brick 
pavements, but it is thought a desirable material in 
this respect. 

It may also be remarked that the danger of a horse 
falling upon any pavement depends very largely upon 
the training of the animal and whether he be accus- 
tomed to the particular surface in question. 



336 A TEXT-BOOK ON ROADS AND PAVEMENTS. 
DURABILITY OF VARIOUS SURFACES. 

The durability of a road or pavement is dependent 
upon so many circumstances connected with local con- 
ditions, the nature of the traffic, methods of con- 
struction, and efficiency of maintenance, that any 
comparison of the various kinds of pavement in this 
respect is difficult and likely to be misleading. 

The qualities which especially affect the durability 
of the road may be partially enumerated as follows: 

(i) The hardness and toughness of the material com- 
posing the surface, upon which depends the resistance 
of the surface to the abrading action of the wheels and 
horses' feet passing over it. 

(2) The firmness of the foundation, which serves to 
distribute the loads over the road-bed and keep the 
surface uniform. 

(3) The drainage of the road-bed, which can only 
properly sustain the loads which come upon it when it 
is dry. 

(4) The permeability of the surface, which should 
form a water-tight covering to serve the purpose of 
keeping the foundation and road-bed in a dry con- 
dition. 

(5) The resistance of the materials of the pavement 
to the disintegrating influences of the atmosphere and 
to the action of the weather. 

The relative importance of these various factors, in 
any particular case, depends largely upon the nature 
and extent of the traffic which is to pass over the 
pavement. 

The amount of traffic to which a street is subjected 
is usually estimated in terms of tons per foot of width 
of street, by observing the number of teams passing a 



CITY STREETS. 337 

given point during certain times, classifying them, and 
assigning an average value of load to each class. The 
wear of the surface will naturally be somewhat propor- 
tional to the amount of traffic. The life of a pave- 
ment is, however, affected by other conditions, and 
hence cannot always be inferred from the amount of 
traffic. 

Traffic may also be classified according to its nature 
as heavy or light, depending upon the weight of indi- 
vidual loads which are carried. It is the heavy loads 
borne upon narrow wheel-tires that do the greatest 
damage to a pavement, and hence the nature rather 
than the amount of traffic determines the character of 
pavement necessary. 

Granite blocks, where a firm unyielding foundation 
is employed, give the hardest and most durable surface 
of any of the common pavements. This is epecially 
the case under very heavy loads. 

The durability of wood-block pavements under wear 
varies widely for the- different types of construction. 
The better grades of treated wood-block pavement seem 
to have given results, in some instances, second only 
to granite blocks, and they are being used under some 
of the heaviest traffic in the larger cities. The older 
and cheaper types of wood pavement are inferior in 
wearing qualities to brick or asphalt. 

Asphalt and brick pavements when well constructed 
are satisfactory under any but the heaviest traffic. 
The relative durability under wear of brick and asphalt 
is a matter of doubt, both materials being subject to 
considerable variations in quality, and showing varying 
results in different localities, due both to differences in 
the quality of the material and in the methods of 
construction. Bitulithic may be classed with asphalt 



338 A TEXT-BOOK ON ROADS AND PAVEMENTS, 

as to durability, although it seems in some instances 
to have shown greater resistance to wear than ordinary 
asphalt. 

Broken stone wears rapidly under moderately heavy 
traffic, and should be employed only on suburban 
streets or country roads used mainly for light driving 
or a small amount of traffic. 

Art. 85. Sources of Revenue for Street 
Improvement. 

Funds required for the improvement of streets in 
cities are commonly derived either from general taxes, 
from assessment upon property in vicinity of the 
improvement, or from a combination of the two. In 
some instances also special taxes are levied upon 
vehicles, or upon business interests which make large 
use of the streets, for the benefit of the paving 
funds. 

Mr. J. L. Van Ornum has brought together* data 
showing the practice in fifty American cities. In a 
few of these the whole charge is placed upon the general 
taxes. In a few, the whole charge is laid upon adjoin- 
ing property, while in a larger number the cost is dis- 
tributed between the two in varying proportions. 
Some cities pay for the intersections of streets from 
general taxes, lajdng the whole cost in the blocks upon 
property fronting the street. Some also pay a share 
(about 20 per cent to 40 per cent) of the cost between 
intersections from general taxes; while in other instances 
the city pays a fixed percentage of the whole cost, the 
remainder being assessed upon the property benefited. 
Some cities pay for the grading of the street from general 

* Transactions American Society of Civil Engineers, Vol. XXXVIIL 



CITY STREETS. 339 

funds, while others include the grading in the cost of 
paving and assess it upon the property. 

There has been considerable discussion on the part of 
municipal officers concerning the proper method of 
apportionment, and many different opinions have been 
advanced as to what should be required in fairness to 
all of the interests involved. Some contend that the 
streets are for general public use, and that the people 
of the city as a whole should pay for their improvement, 
thus ignoring the advantage that the improvement of 
streets may be to the owners of abutting property in 
the increase of values. Others insist that it is fair to 
tax the whole of the improvement upon abutting 
property, claiming that the main benefit is to that 
property, and that when improvement becomes general 
each will have paid his proper proportion of cost. 
Between these two extremes are the larger number who 
recognize the interest of both parties and advocate the 
division of cost between the city as a whole and the 
abutting property in varying proportions. Opinions 
differ as to what these proportions should be, and it is 
evident that the public interest in some streets of a 
city is much greater than in others. Some streets are 
main arteries for travel, others but very little used, and 
the relative values to, the general public and to the 
property owner are very different in the two cases. 

It would be quite impossible to devise any general 
method of apportioning the costs of street work among 
the various interests involved in such a way as to tax 
each in proportion to the benefit derived from the 
improvement. It is generally recognized that the city 
as a whole is interested in the improvement of its streets 
and also that property in the immediate vicinity of an 
improvement is directly benefited thereby. Therefore 



340 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

it may be considered fair and reasonable to tax either 
or both for the improvement. A division of cost would 
without doubt be the more equitable method, but the 
feasibility of securing necessary funds for proper 
improvement by one method or the other must be the 
determining factor in selecting the method. In some 
instances where the funds derived from general taxation 
are closely limited, the assessment of the whole cost of 
street improvements upon abutting property makes 
possible an extent of improvement which would other- 
wise be out of the question, with manifest advantage 
to the property taxed. 

In assessing the cost of street improvement upon 
property in the locality of the work, the usual method 
is to apportion the cost upon abutting property in 
proportion to the frontage upon the street improved. 
Frequently the apportionment is made in proportion 
to area on each side of the street within a certain dis- 
tance of it (sometimes half a block). In a few instances 
a combination of the two methods is used, by which a 
portion of the cost is assessed upon abutting property 
in proportion to frontage and the remainder upon area 
within certain distance. The frontage assessment 
seems reasonably fair and is most commonly employedc 



SHORT-TITLE CATALOGUE 

OF THE 

PUBLICATIONS 

OP 

JOHN WILEY & SONS, 

New York. 
London: CHAPMAN & HALL, Limited. 



ARRANGED UNDER SUBJECTS. 



Descriptive circulars sent on application. Books marked with an asterisk (*) are sold 
at net prices only. All books are bound in cloth unless otherwise stated. 



AGRICULTURE. 



Armsby's Manual of Cattle-feeding nmo, $i 75 

Principles of Animal Nutrition 8vo, 4 00 

Budd and Hansen's American Horticultural Manual: 

Part I. Propagation, Culture, and Improvement nmo, 1 50 

Part II. Systematic Pomology i2mo, 1 50 

Elliott's Engineering for Land Drainage i2mo, 1 50 

Practical Farm Drainage nmo, 1 00 

Graves's Forest Mensuration 8vo, 4 00 

Green's Principles of American Forestry nmo, 1 50 

Grotenfelt's Principles of Modern Dairy Practice. (Wo 11.) nmo, 2 00 

Hanausek's Microscopy of Technical Products. (Winton.) 8vo, 5 00 

Herrick's Denatured or Industrial Alcohol 8vo, 4 00 

Maynard's Landscape Gardening as Applied to Home Decoration. ...... nmo, 1 50 

* McKay and Larsen's Principles and Practice of Butter-making 8vo, 1 50 

Sanderson's Insects Injurious to Staple Crops nmo, 1 50 

*Schwarz's Longleaf Pine in Virgin Forest 12010, 1 25 

Stockbridge's Rocks and Soils 8vo, 2 50 

Winton's Microscopy of Vegetable Foods 8vo, 7 50 

Woll's Handbook for Farmers and Dairymen i6mo, 1 50 



ARCHITECTURE. 

Baldwin's Steam Heating for Buildings nmo, 2 50 

Bashore's Sanitation of a Country House nmo. 1 00 

Berg's Buildings and Structures of American Railroads 4to, 5 00 

Birkmire's Planning and Construction of American Theatres 8vo, 3 00 

Architectural Iron and Steel 8vo, 3 50 

Compound Riveted Girders as Applied in Buildings 8vo, 2 00 

Planning and Construction of High Office Buildings 8vo, 3 50 

Skeleton Construction in Buildings. 8vo, 3 00 

Brigg's Modern American School Buildings 8vo, 4 00 

Carpenter's Heating and Ventilating of Buildings 8vo, 4 00 

1 



Freitag's Architectural Engineering 8vo. 3 50 

Fireproofing of Steel Buildings 8vo, 2 50 

French and Ives's Stereotomy 8vo, 2 50 

Gerhard's Guide to Sanitary House-inspection i6mo, 1 00 

Sanitation of Public Buildings . i2mo, 1 50 

Theatre Fires and Panics i2mo, 1 50 

♦Greene's Structural Mechanics 8vo, 2 50 

Holly's Carpenters' and Joiners' Handbook i8mo, 75 

Johnson's Statics by Algebraic and Graphic Methods 8vo, 2 00 

Kellaway's How to Lay Out Suburban Home Grounds 8vo, 2 00 

Kidder's Architects' and Builders' Pocket-book. Rewritten Edition. i6mo,mor., 5 co 

Merrill's Stones for Building and Decoration . .8vo, 5 00 

Non-metallic Minerals: Their Occurrence and Uses 8vo, 4 00 

Monckton's Stair-building 4to, 4 00 

Patton's Practical Treatise on Foundations 8vo, 5 00 

Peabody's Naval Architecture 8vo, 7 50 

Rice's Concrete-block Manufactur3 8vo, 2 00 

Richey's Handbook for Superintendents of Construction i6mo, mor., 4 00 

* Building Mechanics' Ready Reference Book: 

* Carpenters' and Woodworkers' Edition i6mo, morocco, 1 50 

* Cementworkers and Plasterer's Edition. (In Press.) 

* Stone- and Brick-mason's Edition i2mo, mor., 1 po 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 00 

Siebert and Biggin's Modern Stone-cutting and Masonry 8vo, 1 50 

Snow's Principal Species of Wood 8vo, 3 50 

Sondericker's Graphic Statics with Applications to Trusses, Beams, and Arches. 

8vo, 2 00 

Towne's Locks and Builders' Hardware i8mo, morocco, 3 00 

Turneaure and Maurer's Principles of Reinforced Concrete Construc- 
tion 8vo, 3 00 

Wait's Engineering and Architectural Jurisprudence 8vo, 6 00 

Sheep, 6 50 
Law of Operations Preliminary to Construction in Engineering and Archi- 
tecture 8vo, 5 00 

Sheep, 5 50 

Law of Contracts ." . . 8vo, 3 00 

Wilson's Air Conditioning, (In Press.) 

Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. .8vo, 4 00 
Worcester and Atkinson's Small Hospitals, Establishment and Maintenance, 
Suggestions for Hospital Architecture, with Plans for a Small Hospital. 

i2mo, 1 25 

The World's Columbian Exposition of 1893 Large 4to, 1 00 



ARMY AND NAVY. 

Bernadou's Smokeless Powder, Nitro-cellulose, and the Theory of the Cellulose 

Molecule i2mo, 

Chase's Screw Propellers and Marine Propulsion 8vo, 

Cloke's Gunner's Examiner 8vo, 

Craig's Azimuth 4to, 

Crehore and Squier's Polarizing Photo-chronograph 8vo, 

* Davis's Elements of Law 8vo, 

* Treatise on the Military Law of United States 8vo, 

Sheep, 

De Brack's Cavalry Outposts Duties. (Carr.) 24mo, morocco, 

Dietz's Soldier's First Aid Handbook i6mo, morocco, 

* Dudley's Military Law and the Procedure of Courts-martial. . . Large nmo, 
Durand's Resistance and Propulsion of Ships 8vo, 

2 



2 


5o 


3 


00 


1 


50 


3 


50 


3 


00 


2 


50 


7 


00 


7 


50 


2 


00 


1 


25 


2 


50 


5 


00 



* Dyer's Handbook of Light Artillery i2mo, 

Eissler's Modern High Explosives 8vo, 

* Fiebeger's Text-book on Field Fortification Small 8vo, 

Hamilton's The Gunner's Catechism i8mo, 

* HofP s Elementary Naval Tactics 8vo, 

Ingalls's Handbook of Problems in Direct Fire 8vo, 

* Lissak's Ordnance and Gunnery 8vo, 

* Lyons's Treatise on Electromagnetic Phenomena. Vols. I. and II. .8vo, each, 

* Mahan's Permanent Fortifications. (Mercur.) 8vo, half morocco, 

Manual for Courts-martial i6mo, morocco, 

* Mercur's Attack of Fortified Places i2mo, 

* Elements of the Art of War 8vo, 

Metcalf's Cost of Manufactures — And the Administration of Workshops. .8vo, 

* Ordnance and Gunnery. 2 vols i2mo, 

Murray's Infantry Drill Regulations i8mo, paper, 

Nixon's Adjutants' Manual 24mo, 

Peabody's Naval Architecture 8vo, 

* Phelps's Practical Marine Surveying 8vo, 

Powell's Army Officer's Examiner nmo, 

Sharpe's Art of Subsisting Armies in War i8mo, morocco, 

* Tupes and Poole's Manual of Bayonet Exercises and Musketry Fencing. 

24mo, leather, 

Weaver's Military Explosives 8vo, 

Wheeler's Siege Operations and Military Mining 8vo, 

Winthrop's Abridgment of Military Law i2mo, 

Woodhull's Notes on Military Hygiene i6mo, 

Young's Simple Elements of Navigation i6mo, morocco, 



ASSAYING. 

Fletcher's Practical Instructions in Quantitative Assaying with the Blowpipe. 

nmo, morocco, 

Furman's Manual of Practical Assaying 8vo, 

Lodge's Notes on Assaying and Metallurgical Laboratory Experiments. . . .8vo, 

Low's Technical Methods of Ore Analysis 8vo, 

Miller's Manual of Assaying i2mo, 

Cyanide Process nmo, 

Minet's Production of Aluminum and its Industrial Use. (Waldo.) nmo, 

O'Driscoli's Notes on the Treatment of Gold Ores 8vo, 

Ricketts and Miller's Notes on Assaying 8vo, 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, 

Ulke's Modern Electrolytic Copper Refining 8vo, 

Wilson's Cyanide Processes nmo, 

Chlorination Process nmo, 



ASTRONOMY. 

Comstock's Field Astronomy for Engineers 8vo, 

Craig's Azimuth 4to, 

Crandall's Text-book on Geodesy and Least Squares 8vo, 

Doolittle's Treatise on Practical Astronomy 8vo, 

Gore's Elements of Geodesy 8vo, 

Hayford's Text-book of Geodetic Astronomy 8vo, 

Merriman's Elements of Precise Surveying and Geodesy 8vo, 

* Michie and Harlow's Practical Astronomy 8vo, 

* White's Elements of Theoretical and Descriptive Astronomy nmo, 

3 



3 


00 


4 


00 


2 


00 


I 


00 


I 


50 


4 


00 


6 


00 


6 


00 


7 


So 


1 


50 


2 


00 


4 


00 


5 


00 


5 


00 




10 


1 


00 


7 


50 


2 


50 


4 


00 


I 


50 




50 


3 


00 


2 


00 


2 


50 


1 


50 


2 


00 



1 


50 


3 


00 


3 


00 


3 


OO 


1 


OO 


1 


00 


2 


50 


2 


00 


3 


00 


4 


00 


3 


00 


1 


50 


1 


50 



2 


50 


3 


50 


3 


OO 


4 


OO 


2 


50 


3 


OO 


2 


50 


3 


OO 


2 


OO 



BOTANY. 

Davenport's Statistical Methods, with Special Reference to Biological Variation. 

1 6mo, morocco, i 25 

Thom£ and Bennett's Structural and Physiological Botany i6mo, 2 25 

Westermaier's Compendium of General Botany. (Schneider.) 8vo, 2 00 

CHEMISTRY. 

* Abegg's Theory of Electrolytic Dissociation. (Von Ende.) i2mo, 1 25 

Adriance's Laboratory Calculations and Specific Gravity Tables i2mo, 1 25 

Alexeyeff's General Principles of Organic Synthesis. (Matthews.) 8vo, 3 00 

Allen's Tables for Iron Analysis 8vo, 3 00 

Arnold's Compendium of Chemistry. (Mandel.) Small 8vo, 3 50 

Austen's Notes for Chemical Students i2mo, 1 50 

Beard ' s Mine Gases and Explosions . (In Press. ) 

Bernadou's Smokeless Powder. — Nitro-cellulose, and Theory of the Cellulose 

Molecule i2mo, 2 50 

Bolduan's Immune Sera 12mo , 1 50 

* Browning's Introduction to the Rarer Elements 8vo, 1 50 

Brush and Penfield's Manual of Determinative Mineralogy 8vo, 4 00 

* Claassen's Beet-sugar Manufacture. (Hall and Rolfe.) 8vo, 3 00 

Classen's Quantitative Chemical Analysis by Electrolysis. (Boltwood.). .8vo, 3 00 

Cohn's Indicators and Test-papers i2mo, 2 00 

Tests and Reagents 8vo, 3 00 

Crafts's Short Course in Qualitative Chemical Analysis. (Schaeffer.). . .i2mo, 1 50 

* Danneel's Electrochemistry. (Merriam.) i2mo, 1 25 

Dolezalek's Theory of the Lead Accumulator (Storage Battery). (Von 

Ende.) i2mo, 2 50 

Drechsel's Chemical Reactions. (Merrill.) i2mo, 1 25 

Duhem's Thermodynamics and Chemistry. (Burgess.) 8vo, 4 00 

Eissler's Modern High Explosives 8vo, 4 00 

Effront's Enzymes and their Applications. (Prescott.) 8vo, 3 00 

Erdmann's Introduction to Chemical Preparations. (Dunlap.). ....... i2mo, 1 25 

* Fischer's Physiology of Alimentation Large i2mo. 2 00 

Fletcher's Practical Instructions in Quantitative Assaying with the Blowpipe. 

i2mo, morocco, 1 50 

Fowler's Sewage Works Analyses i2mo, 2 00 

Fresenius's Manual of Qualitative Chemical Analysis. (Wells.) 8vo, 5 00 

Manual of Qualitative Chemical Analysis. Part I. Descriptive. (Wells.) 8vo, 3 00 

Quantitative Chemical Analysis. (Cohn.) 2 vols 8vo, 12 50 

Fuertes's Water and Public Health i2mo, 1 50 

Furman's Manual of Practical Assaying 8vo, 3 00 

* Getman's Exercises in Physical Chemistry i2mo, 2 00 

Gill's Gas and Fuel Analysis for Engineers i2mo, 1 25 

* Gooch and Browning's Outlines of Qualitative Chemical Analysis. Small 8vo, 1 25 

Grotenfelt's Principles of Modern Dairy Practice. (Woll.) i2mo, 2 00 

Groth's Introduction to Chemical Crystallography (Marshall) i2mo, 1 25 

Hammarsten's Text-book of Physiological Chemistry. (Mandel.) 8vo, 4 00 

Hanausek's Microscopy of Technical Products. (Winton. ) 8vo, 5 00 

* Haskin's and MacLeod's Organic Chemistry 12mo, 2 00 

Helm's Principles of Mathematical Chemistry. (Morgan.) nmo, 1 50 

Hering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50 

Herri ck's Denatured or Industrial Alcohol 8vo, 4 00 

Hind's Inorganic Chemistry 8vo, 3 00 

* Laboratory Manual for Students i2mo, 1 00 

Holleman's Text-book of Inorganic Chemistry. (Cooper.) 8vo, 2 50 

Text-book of Organic Chemistry. (Walker and Mott.) 8vo, 2 50 

* Laboratory Manual of Organic Chemistry. (Walker.) nmo, 1 00 

4 



oo 
oo 



Holley and Ladd's Analysis of Mixed Paints, Color Pigments , and Varnishes . 
(In Press) 

Hopkins's Oil-chemists' Handbook 8vo, 3 

Iddings's Rock Minerals 8vo, 5 

Jackson's Directions for Laboratory Work in Physiological Chemistry. .8vo, 1 25 
Johannsen's Key for the Determination of Rock -forming Minerals in Thin Sec- 
tions. (In Press) 

Keep's Cast Iron 8vo, 2 50 

Ladd's Manual of Quantitative Chemical Analysis i2mo, 1 00 

Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 00 

* Langworthy and Austen. The Occurrence of Aluminium in Vegetable 

► Products, Animal Products, and Natural Waters 8vo, 2 00 

Lassar-Cohn's Application of Some General Reactions to Investigations in 

Organic Chemistry. (Tingle.) i2mo, 1 00 

Leach's The Inspection and Analysis of Food with Special Reference to State 

Control 8vo, 

Lob's Electrochemistry of Organic Compounds. (Lorenz.) 8vo, 

Lodge's Notes on Assaying and Metallurgical Laboratory Experiments. .. .8vo, 

Low's Technical Method of Ore Analysis 8vo, 

Lunge's Techno-chemical Analysis. (Cohn.) i2mo 

* McKay and Larsen's Principles and Practice of Butter-making 8vo, 

Maire ' s Modern Pigments and their Vehicles . (In Press. ) 

Mandel's Handbook for Bio-chemical Laboratory i2mo, 

* Martin's Laboratory Guide to Qualitative Analysis with the Blowpipe . . i2mo, 
Mason's Water-supply. (Considered Principally from a Sanitary Standpoint.) 

3d Edition, Rewritten 8vo, 

Examination of Water. (Chemical and Bacteriological.) nmo, 

Matthew's The Textile Fibres. 2d Edition, Rewritten 8vo, 

Meyer's Determination of Radicles in Carbon Compounds. (Tingle.). .i2mo, 

Miller's Manual of Assaying i2mo, 

Cyanide Process nmo, 

Minet's Production of Aluminum and its Industrial Use. (Waldo.) . . . . nmo, 

Mixter's Elementary Text-book of Chemistry nmo, 

Morgan's An Outline of the Theory of Solutions and its Results nmo, 

Elements of Physical Chemistry nmo, 

* Physical Chemistry for Electrical Engineers nmo, 

Morse's Calculations used in Cane-sugar Factories i6mo, morocco, 

* Mu'r's History of Chemical Theories and Laws 8vo, 

Mulliken's General Method for the Identification of Pure Organic Compounds. 

Vol. I Large 8vo, 

O'Driscoll's Notes on the Treatment of Gold Ores 8vo, 

Ostwald's Conversations on Chemistry. Part One. (Ramsey.) nmo, 

" " " " Part Two. (Turnbull.) nmo, 

* Palmer's Practical Test Book of Chemistry 12mo, 

* Pauli's Physical Chemistry in the Service of Medicine. (Fischer.) .... nmo, 

* Penfield's Notes on Determinative Mineralogy and Record of Mineral Tests. 

8vo, paper, 

Pictet's The Alkaloids and their Chemical Constitution. (Biddle.) 8vo, 

Pinner's Introduction to Organic Chemistry. (Austen.) nmo, 

Poole's Calorific Power of Fuels 8vo, 

Prescott and Winslow's Elements of Water Bacteriology, with Special Refer- 
ence to Sanitary Water Analysis nmo, 

* Reisig's Guide to Piece-dyeing 8vo, 

Richards and Woodman's Air, Water, and Food from a Sanitary Standpoint.. 8v o , 

Ricketts and Miller's Notes on Assaying 8vo, 

Rideal's Sewage and the Bacterial Purification of Sewage 8vo, 

Disinfection and the Preservation of Food 8vo, 

Riggs's Elementary Manual for the Chemical Laboratory 8vo, 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, 

5 



7 


50 


3 


OO 


3 


OO 


3 


00 


r 


OO 


1 


50 


1 


50 




60 


4 


00 


1 


25 


4 


00 


I 


00 


T 


00 


I 


00 


2 


50 


I 


50 


I 


00 


3 


00 


5 


00 


1 


50 


4 


00 


5 


00 


2 


00 


1 


50 


2 


00 


1 


00 


1 


25 




50 


5 


00 


1 


50 


3 


00 


T 


25 


'■5 


OO 


2 


OO 


3 


OO 


4 


OO 


4 


OO 


t 


25 


4 


OO 



Ruddiman's Incompatibilities in Prescriptions 8vo, 

* Whys in Pharmacy i2mo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish „ . .8vOi 

Salkowski's Physiological and Pathological Chemistry. (Orndorff.). „ . . .8vo, 
Schimpf's Text-book of Volumetric Analysis i2mo, 

Essentials of Volumetric Analysis. i2mo, 

* Qualitative Chemical Analysis 8vo, 

Smith's Lecture Notes on Chemistry for Dental Students 8vo, 

Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco 

Handbook for Cane Sugar Manufacturers i6mo, morocco, 

Stockbridge's Rocks and Soils 8vo, 

* Tillman's Elementary Lessons in Heat 8vo, 

* Descriptive General Chemistry 8vo» 

Treadwell's Qualitative Analysis. (Hall.) • 8vo r 

Quantitative Analysis. (Hall.) 8vo, 

Turneaure and Russell's Public Water-supplies 8vo, 

Van Deventer's Physical Chemistry for Beginners. (Boltwood.) i2mo, 

* Walke's Lectures on Explosives 8vo, 

Ware's Beet-sugar Manufacture and Refining. Vol. I Small 8vo, 

Vol.11 Small 8vo, 

Washington's Manual of the Chemical Analysis of Rocks 8vo, 

Weaver's Military Explosives 8vo, 

Wehrenfennig's Analysis and Softening of Boiler Feed-Water 8vo, 

Wells's Laboratory Guide in»Qualitative Chemical Analysis 8vo, 

Short Course in Inorganic Qualitative Chemical Analysis for Engineering 

Students nmo, 

Text-book of Chemical Arithmetic i2mo, 

Whipple's Microscopy of Drinking-water 8vo, 

Wilson's Cyanide Processes nmo, 

Chlorination Process i2mo, 

Winton's Microscopy of Vegetable Foods 8vo, 

Wulling's Elementary Course in Inorganic, Pharmaceutical, and Medical 
Chemistry. - nmo, 



CIVIL ENGINEERING. 

BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF ENGINEERING 

RAILWAY ENGINEERING. 

Baker's Engineers' Surveying Instruments nmo, 

Bixby's Graphical Computing Table Paper 19^X24! inches. 

Breed and Hosmer's Principles and Practice of Surveying 8vo, 

* Burr's Ancient and Modern Engineering and the Isthmian Canal 8vo, 

Comstock's Field Astronomy for Engineers 8vo, 

* Corthell's Allowable Pressures on Deep Foundations i2mo, 

Crandall's Text-book on Geodesy and Least Squares 8vo, 

Davis's Elevation and Stadia Tables 8vo, 

Elliott's Engineering for Land Drainage nmo, 

Practical Farm Drainage nmo, 

*Fiebeger's Treatise on Civil Engineering 8vo, 

Flemer's Phototopographic Methods and Instruments 8vo, 

Folwell's Sewerage. (Designing and Maintenance.) 8vo, 

Freitag's Architectural Engineering. 2d Edition, Rewritten 8vo, 

French and Ives's Stereotomy 8vo, 

Goodhue's Municipal Improvements nmo, 

Gore's Elements of Geodesy. . . v 8vo, 

* Hauch and Rice's Tables of Quantities for Preliminary Estimates, i2mo, 

Hayford's Text-book of Geodetic Astronomy 8vo, 

6 



2 


00 


I 


00 


3 


00 


2 


50 


2 


50 


1 


25 


1 


25 


2 


50 


3 


00 


3 


00 


2 


50 


T 


50 


3 


00 


3 


00 


4 


00 


5 


00 


1 


5o 


4 


00 


4 


00 


5- 


CO 


2 


00 


3 


00 


4 


00 


1 


50 


1 


50 


1 


25 


3 


50 


1 


50 


1 


5C 


7 


50 



3 


OO 




25 


3 


OO 


3 


5» 


2 


50 


1 


25 


3 


OO 


1 


OO 


1 


50 


1 


OO 


5 


OO 


5 


OO 


3 


OO 


3 


50 


2 


50 


1 


50 


2 


50 


1 


25 


3 


OO 



Hering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 

Howe's Retaining Walls for Earth i2mo, 

Hoyt and Grover's River Discharge 8vo, 

* Ives's Adjustments of the Engineer's Transit and Level i6mo, Bds. 

Ives and Hilts's Problems in Surveying i6mo, morocco, 

Johnson's (J. B.) Theory and Practice of Surveying Small 8vo, 

Johnson's (L. J.) Statics by Algebraic and Graphic Methods 8vo, 

Laplace's Philosophical Essay on Probabilities. (Truscott and Emory.) . i2mo, 
Mahan's Treatise on Civil Engineering. (1873.) (Wood.) 8vo, 

* Descriptive Geometry. 8vo, 

Merriman's Elements of Precise Surveying and Geodesy 8vo, 

Merriman and Brooks's Handbook for Surveyors i6mo, morocco, 

Nugent's Plane Surveying 8vo, 

Ogden's Sewer Design , i2mo, 

Parsons's Disposal of Municipal Refuse. .. 8vo, 

Patton's Treatise on Civil Engineering 8vo half leather, 

Reed's Topographical Drawing and Sketching 4to, 

Rideal's Sewage and the Bacterial Purification of Sewage 8vo, 

Riemer's Shaft-sinking under Difficult Conditions. (Corning and Peele) . . 8vo, 

Siebert and Biggin's Modern Stone-cutting and Masonry 8vo, 

Smith's Manual of Topographical Drawing. (McMillan.) 8vo, 

Sondericker's Graphic Statics, with Applications to Trusses, Beams, and Arches. 

8vo, 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced 8vo, 

Tracy's Plane Surveying i6mo, morocco, 

* Trautwine's Civil Engineer's Pocket-book i6mo, morocco, 

Venable's Garbage Crematories in America .8vo, 

Wait's Engineering and Architectural Jurisprudence ; 8vo, 

Sheep, 
Law of Operations Preliminary to Construction in Engineering and Archi- 
tecture 8vo, 

Sheep, 

Law of Contracts 8vo, 

Warren's Stereotomy — Problems in Stone-cutting 8vo, 

Webb's Problems in the Use and Adjustment of Engineering Instruments. 

i6mo, morocco, 

Wilson's Topographic Surveying 8vo, 

BRIDGES AND ROOFS. 

Boiler's Practical Treatise on the Construction of Iron Highway Bridges. .8vo, 

Burr and Falk's Influence Lines for Bridge and Roof Computations 8vo, 

Design and Construction of Metallic Bridges 8vo, 

Du Bois's Mechanics of Engineering. Vol. II Small 4to, 

Foster's Treatise on Wooden Trestle Bridges 4to, 

Fowler's Ordinary Foundations 8vo, 

Greene's Roof Trusses 8vo, 

Bridge Trusses 8vo, 

Arches in Wood, Iron, and Stone 8vo, 

Grimm's Secondary Stresses in Bridge Trusses. (In Press.) 

Howe's Treatise on Arches 8vo, 

Design of Simple Roof -trusses in Wood and Steel 8vo, 

Symmetrical Masonry Arches 8vo, 

Johnson, Bryan, and Turneaure's Theory and Practice in the Designing of 

Modern Framed Structures Small 4to, 10 00 

Merriman and Jacoby's Text- book on Roofs and Bridges: 

Part I. Stresses in Simple Trusses 8vo, 2 50 

Part II. Graphic Statics 8vo, 2 50 

Part III. Bridge Design 8vo, 2 50 

Part rv*. Higher Structures 8vo, 2 50 

7 



, 2 


50 


I 


25 


2 


CO 




25 


I 


50 


4 


00 


2 


00 


2 


00 


5 


00 


1 


5o 


2 


50 


2 


00 


3 


5o 


2 


00 


2 


00 


7 


50 


5 


00 


4 


00 


3 


00 


1 


50 


2 


5o 


2 


00 


5 


00 


3 


00 


5 


00 


2 


00 


6 


00 


6 


50 


5 


00 


5 


50 


3 


00 


2 


50 


1 


25 


3 


50 


2 


00 


3 


00 


5 


00 


10 


00 


5 


00 


3 


50 


1 


25 


2 


50 


2 


50 


4 


00 


2 


00 


2 


50 



Morison's Memphis Bridge 4to, 10 oo 

Waddell's De Pontibus, a Pocket-book for Bridge Engineers. . i6mo, morocco, 2 00 

* Specifications for Steel Bridges i2mo, 50 

Wright's Designing of Draw-spans. Two parts in one volume 8vo, 3 50 



HYDRAULICS. 

Barnes's Ice Formation 8vo, 3 00 

Bazin's Experiments upon the Contraction of the Liquid Vein Issuing from 

an Orifice. (Trautwine.). - 8vo, 2 00 

Bovey's Treatise on Hydraulics 8vo, 5 00 

Church's Mechanics of Engineering 8vo , 6 00 

Diagrams of Mean Velocity of Water in Open Channels paper, 1 50 

Hydraulic Motors. . 8vo, 2 00 

Coffin's Graphical Solution of Hydraulic Problems i6mo, morocco, 2 50 

Flather's Dynamometers, and the Measurement of Power i2mo, 3 00 

Folwell's Water-supply Engineering 8vo, 4 00 

Frizell's Water-power 8vo, 5 00 

Fuertes's Water and Public Health i2mo, 1 50 

Water-filtration Works nmo, 2 50 

Ganguillet and Kutter's General Formula for the Uniform Flow of Water in 

Rivers and Other Channels. (Hering and Trautwine.) 8vo, 4 00 

Hazen's Clean Water and How to Get It Large i2mo, l 5o 

Filtration of Public Water-supply 8vo, 3 00 

Hazlehurst's Towers and Tanks for Water- works 8vo, 2 50 

Herschel's 115 Experiments on the Carrying Capacity of Large, Riveted, Metal 

Conduits 8vo, 2 00 

* Hubbard and Kiersted's Water- works Management and Maintenance. . . 8vo, 4 co 
Mason's Water-supply. (Considered Principally from a Sanitary Standpoint.) 

8vo, 4 00 

Merriman's Treatise on Hydraulics 8vo, 5 00 

* Michie's Elements of Analytical Mechanics 8vo, 4 00 

Schuyler's Reservoirs for Irrigation, Water-power, and Domestic Water- 
supply Large 8vo, 5 00 

* Thomas and Watt's Improvement of Rivers 4to, 6 00 

Turneaure and Russell's Public Water-supplies 8vo, 5 00 

Wegmann's Design and Construction of Dams. 5th Edition, enlarged. . .4to, 6 00 

Water-supply of the City of New York from. 1658 to 1895 4to, 10 00 

Whipple's Value of Pure Water Large nmo, 1 00 

Williams and Hazen's Hydraulic Tables 8vo, 1 50 

Wilson's Irrigation Engineering , Small 8vo, 4 00 

Wolff's Windmill as a Prime Mover 8vo, 3 00 

Wood's Turbines 8vo, 2 50 

Elements of Analytical Mechanics . . .8vo, 3 00 



MATERIALS OF ENGINEERING. 

Baker's Treatise on Masonry Construction 8vo. 5 00 

Roads and Pavements 8vo, 5 00 

Black's United States Public Works Oblong 4to, 5 00 

* Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Burr's Elasticity and Resistance of the Materials of Engineering 8vo, 7 50 

Byrne's Highway Construction 8vo, 5 00 

Inspection of the Materials and Workmanship Employed in Construction. 

i6mo, 3 00 

Church's Mechanics of Engineering 8vo, 6 00 

Du Bois's Mechanics of Engineering. Vol. I Small 4to 7 5° 

*Eckel's Cements, Limes, and Plasters 8vo, 6 00 

8 



Johnson's Materials of Construction Large 8vo, 

Fowler's Ordinary Foundations 8vo, 

Graves's Forest Mensuration 8vo, 

* Greene's Structural Mechanics 8vo, 

Keep's Cast Iron 8vo, 

Lanza's Applied Mechanics 8vo, 

Martens's Handbook on Testing Materials. (Henning.) 2 vols 8vo, 

Maurer's Technical Mechanics 8vo, 

Merrill's Stones for Building and Decoration 8vo, 

Merriman's Mechanics of Materials 8vo, 

* Strength of Materials i2mo, 

Metcalf's Steel. A Manual for Steel-users i2mo, 

Patton's Practical Treatise on Foundations 8vo, 

Richardson's Modern Asphalt Pavements 8vo, 

Richey's Handbook for Superintendents of Construction i6mo, mor., 

* Ries's Clays: Their Occurrence, Properties, and Uses 8vo, 

Rockwell's Roads and Pavements in France i2mo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 

♦Schwarz's Longleaf Pine in Virgin Forest ,, nmo, 

Smith's Materials of Machines i2mo, 

Snow's Principal Species of Wood 8vo, 

Spalding's Hydraulic Cement i2mo, 

Text-book on Roads and Pavements i2mo, 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced 8vo, 

Thurston's Materials of Engineering. 3 Parts 8vo, 

Part I. Non-metallic Materials of Engineering and Metallurgy 8vo, 

Part II. Iron and Steel 8vo, 

Part HI. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents 8vo, 

Tillson's Street Pavements and Paving Materials 8vo, 

Turneaure and Maurer's Principles of Reinforced Concrete Construction. 8vo, 
Waddell's De Pontibus. (A Pocket-book for Bridge Engineers.). .i6mo, mor., 

* Specifications for Steel Bridges i2mo, 

Wood's (De V.) Treatise on the Resistance of Materials, and an Appendix on 

the Preservation of Timber 8vo, 

Wood's (De V.) Elements of Analytical Mechanics 8vo, 

Wood's (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and 

Steel , 8vo, 4 00 



RAILWAY ENGINEERING. 

Andrew's Handbook for Street Railway Engineers 3x5 inches, morocco, 

Berg's Buildings and Structures of American Railroads 4to, 

Brook's Handbook of Street Railroad Location i6mo, morocco, 

Butt's Civil Engineer's Field-book i6mo, morocco, 

Crandall's Transition Curve i6mo, morocco, 

Railway and Other Earthwork Tables 8vo, 

Crookett's Methods for Earthwork Computations. (In Press) 

Dawson's "Engineering" and Electric Traction Pocket-book. . i6mo, morocco 

Dredge's History of the Pennsylvania Railroad: (1879) Paper, 

Fisher's Table of Cubic Yards Cardboard, 

Godwin's Railroad Engineers' Field-book and Explorers' Guide. . . i6mo, mor., 
Hudson's Tables for Calculating the Cubic Contents of Excavations and Em- 
bankments 8vo, 

Molitor and Beard's Manual for Resident Engineers i6mo, 

Nagle's Field Manual for Railroad Engineers i6mo, morocco, 

Philbrick's Field Manual for Engineers i6mo, morocco, 

Raymond's Elements of Railroad Engineering. (In Press.) 

9 



6 


OO 


3 


So 


4 


00 


2 


50 


2 


50 


7 


50 


7 


50 


4 


00 


5 


00 


5 


00 


1 


00 


2 


00 


5 


00 


3 


00 


4 


00 


5 


00 


1 


25 


3 


00 


1 


25 


1 


00 


3 


50 


2 


00 


2 


00 


5 


00 


8 


00 


2 


00 


3 


50 


2 


50 


4 


00 


3 


00 


2 


00 




50 


2 


00 


3 


00 



r 


25 


5 


00 


1 


50 


2 


50 


1 


50 


1 


50 


5 


00 


5 


00 




25 


2 


50 


1 


00 


i 


00 


3 


00 


3 


00 



Searles's Field Engineering i6mo, morocco, 3 00 

Railroad Spiral i6mo, morocco, 1 50 

Taylor's Prismoidal Formulae and Earthwork 8vo, 1 50 

* Trautwine's Method of Calculating the Cube Contents of Excavations and 

Embankments by the Aid of Diagrams 8vo, 2 00 

The Field Practice of Laying Out Circular Curves for Railroads. 

1 2 mo, morocco, 2 50 

Cross-section Sheet Paper, 23 

Webb's Railroad Construction i6mo, morocco, 5 00 

Economics of Railroad Construction Large i2mo, 2 50 

Wellington's Economic Theory of the Location of Railways Small 8vo.» 5 00 



DRAWING. 

Barr's Kinematics of Machinery 8vo, 

* Bartlett's Mechanical Drawing. 8vo, 

* " " " Abridged Ed 8vo, 

Coolidge's Manual of Drawing 8vo, paper, 

Coolidge and Freeman's Elements of General Drafting for Mechanical Engi- 
neers Oblong 4to> 

Durley's Kinematics of Machines 8vo, 

Emch's Introduction to Projective Geometry and its Applications 8vo, 

Hill's Text-book on Shades and Shadows, and Perspective 8vo, 

Jamison's Elements of Mechanical Drawing 8vo, 

Advanced Mechanical Drawing 8vo, 

Jones's Machine Design: 

Part I. Kinematics of Machinery 8vo, 

Part II. Form, Strength, and Proportions of Parts 8vo, 

MacCord's Elements of Descriptive Geometry 8vo, 

Kinematics; or, Practical Mechanism 8vo, 

Mechanical Drawing 4to, 

Velocity Diagrams 8vo, 

MacLeod's Descriptive Geometry. Small 8vo-, 

* Mahan's Descriptive Geometry and Stone-cutting 8vo, 

Industrial Drawing. (Thompson.) 8vo, 

Moyer's Descriptive Geometry 8vo, 

Reed's Topographical Drawing and Sketching 4to, 

Reid's Course in Mechanical Drawing 8vo, 

Text-book of Mechanical Drawing and Elementary Machine Design. 8vo, 

Robinson's Principles of Mechanism 8vo, 

Schwamb and Merrill's Elements of Mechanism 8vo, 

Smith's (R. S.) Manual of Topographical Drawing. (McMillan.) 8vo, 

Smith (A. W.) and Marx's Machine Design 8vo, 

* Titsworth's Elements of Mechanical Drawing Oblong 8vo, 

Warren's Elements of Plane and Solid Free-hand Geometrical Drawing. i2mo, 

Drafting Instruments and Operations i2mo, 

Manual of Elementary Projection Drawing nmo, 

Manual of Elementary Problems in the Linear Perspective of Form and 

Shadow i2mo, 

Plane Problems in Elementary Geometry i2mo, 

Elements of Descriptive Geometry, Shadows, and Perspective 8vo, 

General Problems of Shades and Shadows 8vo, 

Elements of Machine Construction and Drawing 8vo, 

Problems, Theorems, and Examples in Descriptive Geometry 8vo, 

Weisbach's Kinematics and Power of Transmission. (Hermann and 

Klein.) i . . .? 8vo, 

Whelpley's Practical Instruction in the Art of Letter Engraving i2mo, 

Wilson's (H. M.) Topographic Surveying 8vo, 

10 



2 


50 


3 


00 


1 


50 


1 


00 


2 


SO 


4 


00 


2 


5o 


2 


00 


2 


50 


2 


00 


I 


50 


3 


00 


3 


00 


5 


00 


4 


00 


1 


5o 


1 


5o 


1 


50 


3 


50 


2 


00 


5 


00 


2 


00 


3 


00 


3 


00 


3 


00 


2 


5o 


3 


00 


1 


25 


1 


00 


1 


25 


1 


50 


1 


00 


1 


25 


3 


50 


3 


00 


7 


50 


2 


50 


5 


oo 


2 


00 


3 


50 



Wilson's (V. T.) Free-hand Perspective 8vo, 2 50 

Wilson's (V. T.) Free-hand Lettering 8vo, 1 00 

Woolf' s Elementary Course in Descriptive Geometry Large 8vo, 3 00 

ELECTRICITY AND PHYSICS. 

* Abegg's Theory of Electrolytic Dissociation. (Von Ende.) i2mo, 

Anthony and Brackett's Text-book of Physics. (Magie.) Small 8vo, 

Anthony's Lecture-notes on the Theory of Electrical Measurements. . . . i2mo, 
Benjamin's History of Electricity 8vo, 

Voltaic Cell 8vo, 

Betts's Lead Refining and Electrolysis. (In Press.) 

Classen's Quantitative Chemical Analysis by Electrolysis. (Boltwood.).8vo, 

* Collins's Manual of Wireless Telegraphy i2mo, 

Morocco, 
Crehore and Squier's Polarizing Photo-chronograph 8vo, 

* Danneel's Electrochemistry. (Merriam.). i2mo, 

Dawson's "Engineering" and Electric Traction Pocket-book. i6mo, morocco, 
Dolezalek's Theory of the Lead Accumulator (Storage Battery). (Von Ende.) 

i2mo, 

Duhem's Thermodynamics and Chemistry. (Burgess.) 8vo, 

Flather's Dynamometers, and the Measurement of Power i2mo, 

Gilbert's De Magnete. (Mottelay.) 8vo, 

Hanchett's Alternating Currents Explained. . __ i2mo, 

Hering's Ready Reference Tables (Conversion Factors) iomo, morocco, 

Hobart and Ellis's High-speed Dynamo Electric Machinery. (In Press.) 

Holman's Precision of Measurements 8vo, 

Telescopic Mirror-scale Method, Adjustments, and Tests. . . Large 8vo, 
Karapetoff's Experimental Electrical Engineering. (In Press.) 

Kinzbrunner's Testing of Continuous-current Machines 8vo, 

Landauer's Spectrum Analysis. (Tingle.) 8vo, 

Le Chateliers High-temperature Measurements. (Boudouard — Burgess.) i2mo, 
Lob's Electrochemistry of Organic Compounds. (Lorenz.) 8vo, 

* Lyons'3 Treatise on Electromagnetic Phenomena. Vols. I. and II. 8vo, each, 

* Michie's Elements of Wave Motion Relating to Sound and Light 8vo, 

Niaudet's Elementary Treatise on Electric Batteries. (Fishback.) i2mo, 

Norris's Introduction to the Study of Electrical Engineering. (In Press.) 

* Parshall and Hobart's Electric Machine Design 4T0, half morocco, 12 50 

Reagan's Locomotives: Simple, Compound, and Electric. New Edition. 

Large nmo, 3 50 

* Rosenberg's Electrical Engineering. (Haldane Gee— Kinzbrunner. ). . .8vo, 2 00 

Ryan, Norris, and Hoxie's Electrical Machinery. Vol. 1 8vo, 

Thurston's Stationary Steam-engines 8vo, 

* Tillman's Elementary Lessons in Heat 8vo, 

Tory and Pitcher's Manual of Laboratory Physics Small 8vo, 

Ulke's Modern Electrolytic Copper Refining 8vo, 

LAW. 

* Davis's Elements of Law 8vo, 

* Treatise on the Military Law cf United States 8vo, 

* Sheep, 

* Dudley's Military Law and the Procedure of Courts-martial . . . Large nmo, 

Manual for Courts-martial i6mo, morocco. 

Wait's Engineering and Architectural Jurisprudence 8vo, 

Sheep, 
Law of Operations Preliminary to Construction in Engineering and Archi- 
tecture 8vo 

Sheep, 

Law of Contracts 8vo, 

Winthrop's Abridgment of Military Law nmo, 

11 



I 


25 


3 


OO 


1 


OO 


3 


OO 


3 


OO 


3 


OO 


1 


50 


2 


OO 


3 


OO 


1 


25 


5 


OO 


2 


50 


4 


00 


3 


CO 


2 


50 


1 


OO 


2 


So 


2 


OO 




75 


2 


OO 


3 


OO 


3 


OO 


3 


OO 


6 


OO 


4 


OO 


2 


50 



2 


50 


2 


50 


I 


50 


2 


OO 


3 


OO 


2 


50 


7 


OO 


7 


50 


2 


50 


I 


50 


6 


00 


6 


50 


5 


OO 


5 


50 


3 


OO 


2 


50 



MANUFACTURES. 

Bernadou's Smokeless Powder — Nitro-cellulose and Theory of the Cellulose 

Molecule. nmo, 

Holland's Iron Founder i2mo, 

The Iron Founder," Supplement nmo, 

Encyclopedia of Founding and Dictionary of Foundry Terms Used in the 
Practice of Moulding nmo, 

* Claassen's Beet-sugar Manufacture. (Hall and Rolfe.) 8vo, 

* Eckel's Cements, Limes, and Plasters 8vo, 

Eissler's Modern High Explosives 8vo, 

Effront's Enzymes and their Applications. (Prescott.) 8vo, 

Fitzgerald's Boston Machinist. . i2mo, 

Ford's Boiler Making for Boiler Makers i8mo. 

Herrick's Denatured or Industrial Alcohol *8vo, 

HoUey and Ladd's Analysis of Mixed Paints, Color Pigments, and Varnishes. 

(In Press.) 

Hopkins's Oil-chemists' Handbook 8vo, 

Keep's Cast Iron 8vo, 

Leach's The Inspection and Analysis of Food with Special Reference to State 
Control Large 8vo, 

* McKay and Larsen's Principles and Practice of Butter-making 8vo, 

Maire's Modern Pigments and their Vehicles. (In Press.) 

Matthews's The Textile Fibres. • 2d Edition, Rewritten 8vo, 

Metcalf's Steel. A Maunal for Steel-users nmo, 

Metcalfe's Cost of Manufactures — And the Administration of Workshops . . 8vo, 

Meyer's Modern Locomotive Construction 4to, 

Morse's Calculations used in Cane-sugar Factories i6mo, morocco, 

* Reisig's Guide to Piece-dyeing 8vo, 

Rice's Concrete-block Manufacture 8vo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 

Smith's Press-working of Metals 8vo, 

Spalding's Hydraulic Cement i2mo, 

Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco, 

Handbook for Cane Sugar Manufacturers i6mo, morocco, 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced 8vo, 

Thurston's Manual of Steam-boilers, their Designs, Construction and Opera- 
tion 8vo, 

Ware's Beet-sugar Manufacture and Refining. Vol. I Small 8vo, 

Vol. II 8vo, 

Weaver's Military Explosives 8vo, 

West's American Foundry Practice nmo, 

Moulder's Text-book nmo, 

Wolff's Windmill as a Prime Mover 8vo, 

Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel . 8vo, 

MATHEMATICS. 

Baker's Elliptic Functions 8vo, 

Briggs's Elements of Plane Analytic Geometry 1 2mo, 

Buchanan's Plane and Spherical Trigonometry. (In Press.) 

Compton's Manual of Logarithmic Computations nmo, 

Davis's Introduction to the Logic of Algebra 8vo, 

* Dickson's College Algebra Large nmo, 

* Introduction to the Theory of Algebraic Equations Large nmo, 

Emch's Introduction to Projective Geometry and its Applications 8vo, 

Halsted's Elements of Geometry . .""I •. . .8vo, 

Elementary Synthetic Geometry 8vo, 

* Rational Geometry nmo, 

12 



2 


50 


2 


50 


2 


50 


3 


OO 


3 


OO 


6 


00 


4 


OO 


3 


OO 


1 


OO 


I 


OO 


4 


00 


3 


OO 


2 


50 


7 


50 


1 


50 


4 


OO 


2 


OO 


5 


OO 


10 


OO 


1 


50 


25 


OO 


2 


OO 


3 


OO 


3 


OO 


2 


OO 


3 


OO 


3 


OO 


5 


OO 


5 


OO 


4 


OO 


5 


OO 


3 


OO 


2 


50 


2 


50 


3 


OO 


4 


OO 



I 


50 


I 


OO 


I 


So 


I 


50 


I 


50 


1 


25 


2 


50 


1 


75 


1 


50 


I 


50 





15 


5 


oo 




25 


2 


oo 


3 


oo 


I 


5o 


I 


oo 


3 


5o 


3 


00 


i 


5o 


3 


oo 


2 


oo 


3 


oo 


2 


oo 


I 


oo 



* Johnson's (J. B.) Three-place Logarithmic Tables: Vest-pocket size. paper, 

100 copies for 

* Mounted on heavy cardboard, 8 X io inches, 

io copies for 
Johnson's (W. W.) Elementary Treatise on Differential Calculus. Small 8vo, 

Elementary Treatise on the Integral Calculus Small 8vo, 

Johnson's (W. W.) Curve Tracing in Cartesian Co-ordinates i2mo, 

Johnson's (W. W.) Treatise on Ordinary and Partial Differential Equations. 

Small 8vo, 

Johnson's Treatise on the Integral Calculus Small 8vo, 

Johnson's (W. W.) Theory of Errors and the Method of Least Squares. i2mo, 

* Johnson's (W. W.) Theoretical Mechanics i2mo, 

Laplace's Philosophical Essay on Probabilities. (Truscott and Emory. ).i2mo, 

* Ludlow and Bass. Elements of Trigonometry and Logarithmic and Other 

Tables 8vo, 

Trigonometry and Tables published separately Each, 

* Ludlow's Logarithmic and Trigonometric Tables 8vo, 

Manning's IrrationalN umbers and their Representation bySequences and Series 

i2mo, i 25 
Mathematical Monographs. Edited by Mansfield Merriman and Robert 

S. Woodward Octavo, each 1 00 

No. 1. History of Modern Mathematics, by David Eugene Smith. 
No. 2. Synthetic Projective Geometry, by George Bruce Halsted. 
Ko. 3. Determinants, by Laenas Gifford Weld. No. 4. Hyper- 
bolic Functions, by James McMahon. No. 5„ Harmonic Func- 
tions, by William E. Byerly. No. 6. Grassmann's Space Analysis, 
by Edward W. Hyde. No. 7. Probability and Theory of Errors, 
by Robert S. Woodward. No. 8. Vector Analysis and Quaternions, 
by Alexander Macfarlane. No. o. Differential Equations, by 
William Woolsey Johnson. No. 10. The Solution of Equations, 
by Mansfield Merriman. No. n. Functions of a Complex Variable, 
by Thomas S. Fiske. 

Maurer's Technical Mechanics 8vo, 

Merriman's Method of Least Squares 8vo, 

Rice and Johnson's Elementary Treatise on the Differential Calculus. . Sm. 8vo, 
Differential and Integral Calculus. 2 vols, in one Small 8vo, 

* Veblen and Lennes's Introduction to the Real Infinitesimal Analysis of One 

Variable 8vo, 

Wood's Elements of Co-ordinate Geometry 8vo, 

Trigonometry: Analytical, Plane, and Spherical nmo, 



MECHANICAL ENGINEERING. 

MATERIALS OF ENGINEERING, STEAM-ENGINES AND BOILERS. 

Bacon's Forge Practice nmo, 

Baldwin's Steam Heating for Buildings nmo, 

Barr's Kinematics of Machinery 8vo, 

* Bartlett's Mechanical Drawing 8vo, 

* " " " Abridged Ed 8vo, 

Benjamin's Wrinkles and Recipes nmo, 

Carpenter's Experimental Engineering 8vo, 

Heating and Ventilating Buildings 8vo, 

Clerk's Gas and Oil Engine Small 8vo, 

Coolidge's Manual of Drawing , 8vo, paper, 

Coolidge and Freeman's Elements of General Drafting for Mechanical En- 
gineers Oblong 4T0, 

Cromwell's Treatise on Toothed Gearing nmo, 

Treatise on Belts and Pulleys nmo, 

13 



4 


OO 


2 


OO 


3 


OO 


-> 


SO 


2 


OO 


2 


OO 


I 


OO 



I 


50 


2 


50 


2 


50 


3 


00 


I 


50 


2 


00 


6 


00 


4 


00 


4 


00 


1 


00 


2 


50 


1 


50 


1 


50 



Durley's Kinematics of Machines 8vo, 4 00 

Flather's Dynamometers and the Measurement of Power. i2mo, 3 00 

Rope Driving i2mo, 2 00 

Gill's Gas and Fuel Analysis for Engineers i2mo, 1 25 

Hall's Car Lubrication i2mo, 1 00 

Hering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50 

Hutton's The Gas Engine 8vo, 5 00 

Jamison's Mechanical Drawing 8vo, 2 50 

Jones's Machine Design: 

Part I. Kinematics of Machinery 8vo, 1 50 

Part II. Form, Strength, and Proportions of Parts 8vo, 3 00 

Kent's Mechanical Engineers' Pocket-book i6mo, morocco, 5 00 

Kerr's Power and Power Transmission 8vo, 2 00 

Leonard's Machine Shop, Tools, and Methods 8vo, 4 00 

* Lorenz's Modern Refrigerating Machinery. (Pope, Haven, and Dean.) . .8vo, 4 00 
MacCord's Kinematics; or, Practical Mechanism 8vo, 5 00 

Mechanical Drawing 4to, 4 00 

Velocity Diagrams 8vo, 1 50 

MacFar land's Standard Reduction Factors for Gases 8vo, 1 50 

Mahan's Industrial Drawing. (Thompson.) 8vo, 3 50 

Poole's Calorific Power of Fuels 8vo, 3 00 

Reid's Course in Mechanical Drawing 8vo, 2 00 

Text-book of Mechanical Drawing and Elementary Machine Design. 8vo, 3 00 

Richard's Compressed Air nmo, 1 50 

Robinson's Principles of Mechanism 8vo, 3 00 

Schwamb and Merrill's Elements of Mechanism 8vo, 3 00 

Smith's (O.) Press-working of Metals 8vo, 3 00 

Smith (A. W.) and Marx's Machine Design 8vo, 3 00 

Thurston's Treatise on Friction and Lost Work in Machinery and Mill 

Work 8vo, 3 00 

Animal as a Machine and Prime Motor, and the Laws of Energetics . nmo, 1 00 

Tillson's Complete Automobile Instructor i6mo, 1 50 

Morocco, 2 00 

Warren's Elements of Machine Construction and Drawing 8vo, 7 50 

Weisbach's Kinematics and the Power of Transmission. (Herrmann — 

Klein.) 8vo, 5 00 

Machinery of Transmission and Governors. (Herrmann — Klein.). .8vo, 5 00 

Wolff's Windmill as a Prime Mover 8vo, 3 00 

Wood's Turbines 8vo, 2 50 

MATERIALS OF ENGINEERING. 

* Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Burr's Elasticity and Resistance of the Materials of Engineering. 6th Edition. 

Reset 8vo, 7 50 

Church's Mechanics of Engineering 8vo, 6 00 

* Greene's Structural Mechanics 8vo, 2 50 

Johnson's Materials of Construction 8vo, 6 00 

Keep's Cast Iron 8vo, 2 50 

Lanza's Applied Mechanics 8vo, 7 50 

Martens's Handbook on Testing Materials. (Henning.) 8vo, 7 50 

Maurer's Technical Mechanics 8vo, 4 00 

Merriman's Mechanics of Materials 8vo, 5 00 

* Strength of Materials i2mo, 1 00 

Metcalf's Steel. A Manual for Steel-users nmo, 2 00 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 00 

Smith's Materials of Machines nmo, 1 00 

Thurston's Materials of Engineering^ 3 vols., 8vo, 8 00 

Part II. Iron and Steel. . .> 8vo, 3 50 

Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents 8vo, 2 50 

14 



Wood's (De V.) Treatise on the Resistance of Materials and an Appendix on 

the Preservation of Timber .8vo, 2 00 

Elements of Analytical Mechanics 8vo, 3 00" 

Wood's (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and 

Steel 8vo, 4 00 

STEAM-ENGINES AND BOILERS. 

Berry's Temperature-entropy Diagram i2mo, 1 25 

Carnot's Reflections on the Motive Power of Heat. (Thurston.) i2mo, 1 50 

Creighton's Steam-engine and other Heat-motors . 8vo, 500 

Dawson's "Engineering" and Electric Traction Pocket-book. . . .i6mo, mor., 5 00 

Ford's Boiler Making for Boiler Makers i8mo, 1 00 

Goss's Locomotive Sparks 8vo, 2 00 

Locomotive Performance 8vo, 5 00 

Hemenway's Indicator Practice and Steam-engine Economy i2mo, 2 00 

Hutton's Mechanical Engineering of Power Plants 8vo, 5 00 

Heat and Heat-engines 8vo, 5 00 

Kent's Steam boiler Economy 8vo, 4 00 

Kneass's Practice and Theory of the Injector 8vo, 1 50 

MacCord's Slide-valves 8vo, 2 00 

Meyer's Modern Locomotive Construction 4to, 10 oa 

Peabody's Manual of the Steam-engine Indicator i2mo, 1 50 

Tables of the Properties of Saturated Steam and Other Vapors 8vo, 1 00 

Thermodynamics of the Sttam-engine and Other Heat-engines 8vo, 5 00 

Valve-gears for Steam-engines 8vo, 2 50 

Peabody and Miller's Steam-boilers 8vo, 4 00 

Pray's Twenty Years with the Indicator Large 8vo, 2 50 

Pupin's Thermodynamics of Reversible Cycles in Gases and Saturated Vapors. 

(Osterberg.) nmo, 1 25 

Reagan's Locomotives: Simple, Compound, and Electric. New Edition. 

Large i2mo, 3 50 

Sinclair's Locomotive Engine Running and Management i2mo, 2 00 

Smart's Handbook of Engineering Laboratory Practice i2mo, 2 50 

Snow's Steam-boiler Practice. 8vo, 3 00 

Spangler's Valve-gears 8vo, 2 50 

Notes on Thermodynamics i2mo, 1 00 

Spangler, Greene, and Marshall's Elements of Steam-engineering 8vo, 3 00 

Thomas's Steam-turbines 8vo, 3 50 

Thurston's Handy Tables 8vo, 1 50 

Manual of the Steam-engine 2 vols., 8vo, 10 00 

Part I. History, Structure, and Theory. 8vo, 6 00 

Part II. Design, Construction, and Operation 8vo, 6 00 

Handbook of Engine and Boiler Trials, and the Use of the Indicator and 

the Prony Brake 8vo, 5 00 

Stationary Steam-engines 8vo, 2 50 

Steam-boiler Explosions in Theory and in Practice i2mo, 1 50 

Manual of Steam-boilers, their Designs, Construction, and Operation. 8vo, 5 00 
Wehrenfenning's Analysis and Softening of Boiler Feed-water (Patterson) 8vo, 4 00 

Weisbach's Heat, Steam, and Steam-engines. (Du Bois.) 8vo, 5 00 

Whitham's Steam-engine Design 8vo, 5 00 

Wood's Thermodynamics, Heat Motors, and Refrigerating Machines. . .8vo, 4 00 



MECHANICS AND MACHINERY. 

Barr's Kinematics of Machinery 8vo, 2 50 

* Bovey : s Strength of Materials and Theory of Structures 8vo, 7 50 

Chase's The Art of Pattern-making nmo, 2 50 

15 



6 


OO 


2 


oo 


I 


50 


I 


SO 


I 


50 


I 


50 


I 


50 


2 


oo 



3 


50 


4 


oo 


7 


50 


IO 


oo 


4 


oo 


i 


oo 


3 


oo 


2 


oo 


2 


oo 


5 


oo 


2 


50 


I 


oo 



Church's Mechanics of Engineering 8vo, 

Notes and Examples in Mechanics 8vo, 

Compton's First Lessons in Metal-working i2mo, 

Compton and De Groodt's The Speed Lathe nmo, 

Cromwell's Treatise on Toothed Gearing i2mo, 

Treatise on Belts and Pulleys , i2mo, 

Dana's Text-book of Elementary Mechanics for Colleges and Schools. . nmo, 

Dingey's Machinery Pattern Making nmo, 

Dredge's Record of the Transportation Exhibits Building of the World's 

Columbian Exposition of 1893 4to half morocco, 5 00 

Du Bois's Elementary Principles of Mechanics : 

Vol. I. Kinematics 8vo, 

Vol. II. Statics 8vo, 

Mechanics of Engineering. Vol. I Small 4to, 

Vol. II Small 4to, 

Durley's Kinematics of Machines 8vo, 

Fitzgerald's Boston Machinist i6mo, 

Flather's Dynamometers, and the Measurement of Power nmo, 

Rope Driving nmo, 

Goss's Locomotive Sparks 8vo, 

Locomotive Performance 8vo, 

* Greene's Structural Mechanics 8vo, 

Hall's Car Lubrication nmo, 

Hobart and Ellis's High-speed Dynamo Electric Machinery. (In Press.) 

Holly's Art of Saw Filing i8mo, 75 

James's Kinematics of a Point and the Rational Mechanics of a Particle. 

Small 8vo, 

* Johnson's (W. W.) Theoretical Mechanics nmo, 

Johnson's (L. J.) Statics by Graphic and Algebraic Methods 8vo, 

Jones's Machine Design: 

Part I. Kinematics of Machinery 8vo, 

Part II. Form, Strength, and Proportions of Parts 8vo, 

Kerr's Power and Power Transmission 8vo, 

Lanza's Applied Mechanics : . . . 8vo, 

Leonard's Machine Shop, Tools, and Methods 8vo, 

* Lorenz's Modern Refrigerating Machinery. (Pope, Haven, and Dean.) .8vo, 
MacCord's Kinematics; or, Practical Mechanism 8vo, 

Velocity Diagrams 8vo, 

* Martin's Text Book on Mechanics, Vol. I, Statics nmo, 

* Vol. 2, Kinematics and Kinetics . .i2mo, 

Maurer's Technical Mechanics 8vo, 

Merriman's Mechanics of Materials 8vo, 

* Elements of Mechanics nmo, 

* Michie's Elements of Analytical Mechanics 8vo, 

* Parshall and Hobart's Electric Machine Design 4to, half morocco, 

Reagan's Locomotives : Simple, Compound, and Electric. New Edition. 

Large nmo, 
Reid's Course in Mechanical Drawing 8vo, 

Text-book of Mechanical Drawing and Elementary Machine Design. 8vo, 

Richards's Compressed Air nmo, 

Robinson's Principles of Mechanism 8vo, 

Ryan, Norris, and Hoxie's Electrical Machinery. Vol. I .8vo, 

Sanborn's Mechanics : Problems . Large nmo, 

Schwamb and Merrill's Elements of Mechanism 8vo, 

Sinclair's Locomotive-engine Running and Management nmo, 

Smith's (O.) Press-working of Metals 8vo, 

Smith's (A. W.) Materials of Machines nmo, 

Smith (A. W.) and Marx's Machine Design , 8vo, 

Sorel' s Carbureting and Combustion of Alcohol Engines. (Woodward and 

Preston.) Large 8vo, 3 00 

16 



2 


OO 


3 


OO 


2 


00 


I 


50 


3 


OO 


2 


OO 


7 


50 


4 


OO 


4 


OO 


5 


OO 


1 


50 


1 


25 


1 


SO 


4 


OO 


5 


OO 


1 


OO 


4 


OO 


12 


50 


3 


5o 


2 


OO 


3 


00 


I 


50 


3 


OO 


2 


50 


1 


SO 


3 


00 


2 


00 


3 


00 


1 


00 


3 


00 



SpangJer, Greene, and Marshall's Elements of Steam-engineering 8vo, 3 00 

Thurston's Treatise on Friction and Lost Work in Machinery and Mill 

Work 8vo, 3 00 

Animal as a Machine and Prime Motor, and the Laws of Energetics. i2mo, 1 00 

Tillson's Complete Automobile Instructor , i6mo, 1 50 

Morocco, 2 00 

Warren's Elements of Machine Construction and Drawin: 8vo, 7 50 

Weisbach's Kinematics and Power of Transmission. (Herrmann — Klein. ).8vo. 5 00 

Machinery of Transmission and Governors. (Herrmann — Klein. ).8vo. 5 00 

Wood's Elements of Analytical Mechanics 8vo, 3 00 

Principles of Elementary Mechanics i2mo, 1 25 

Turbines 8vo, 2 50 

The World's Columbian Exposition of 1893 4to, 1 00 

MEDICAL. 

* Bolduan's Immune Sera 12mo, 

De Fursac's Manual of Psychiatry. (Rosanoff and Collins.). . . Large nmo, 
Ehrlich's Collected Studies on Immunity. (Bolduan.) 8vo, 

* Fischer's Physiology of Alimentation Large l2mo, cloth, 

Hammarsten's Text-book on Physiological Chemistry. (Mandel. ) 8vo, 

Lassar-Cohn's Practical Urinary Analysis. (Lorenz.) : . .i2mo, 

* Pauli's Physical Chemistry in the Service of Medicine. (Fischer. - ) . . nmo, 

* Pozzi-Escot's The Toxins and Venoms and their Antibodies. (Conn.), nmo, 

Rostoski's Serum Diagnosis. (Bolduan.) .nmo, 

Salkowski's Physiological and Pathological Chemistry. (Orndorff.) 8vo, 

* Satterlee's Outlines of Human Embryology 12 mo, 

Steel's Treatise on the Diseases of the Dog 8vo, 

Von Behring's Suppression of Tuberculosis. (Bolduan.) i2mo, 

Woodhull's Notes on Military Hygiene i6mo, 

* Personal Hygiene nmo, 

Wulling's An Elementary Course in Inorganic Pharmaceutical and Medical 

Chemistry nmo, 2 00 

METALLURGY. 

Betts's Lead Refining by Electrolysis. (In Press.) 

Egleston's Metallurgy of Silver, Gold, and Mercury: 

Vol. I. Silver 8vo, 7 50 

Vol. II. Gold and Mercury 8vo, 7 50 

Goesel's Minerals and Metals: A Reference Book , . . . . i6mo, mor. 3 00 

* Iles's Lead-smelting nmo, 2 50 

Keep's Cast Iron , 8vo, 2 50 

Kunhardt's Practice of Ore Dressing in Europe 8vo, 1 50 

Le Chatelier's High-temperature Measurements. (Boudouard — Burgess. )nmo, 3 00 

Metcalf's Steel. A Manual for Steel-users nmo, 2 00 

Miller's Cyanide Process nmo, 1 00 

Minet's Production of Aluminum and its Industrial Use. (Waldo.). . . . nmo, 2 50 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, 4 00 

Smith's Materials of Machines nmo, 1 00 

Thurston's Materials of Engineering. In Three Parts 8vo, 8 00 

Part II. Iron and Steel 8vo, 3 50 

Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents 8vo, 2 50 

Ulke's Modern Electrolytic Copper Refining 8vo, 3 00 

MINERALOGY. 

Barringer's Description of Minerals of Commercial Value. Oblong, morocco, 2 50 

Boyd's Resources of Southwest Virginia 8vo, 3 00 

17 



1 


50 


2 


SO 


6 


OO 


2 


00 


4 


OO 


1 


OO 


1 


25 


1 


OO 


1 


OO 


2 


50 


I 


25 


3 


50 


1 


00 


I 


50 


1 


00 



Boyd's Map of Southwest Virignia Pocket-book form. 

♦Browning's Introduction to the Rarer Elements 8vo, 

Brush's Manual of Determinative Mineralogy. (Penfield.) 8vo, 

Chester's Catalogue of Minerals. . . 8vo, paper, 

Cloth, 

Dictionary of the Names of Minerals 8vo, 

Dana's System of Mineralogy Large 8vo, half leather, 12 

First Appendix to Dana's New " System of Mineralogy." Large 8vo, 

Text-book of Mineralogy 8vo, 

Minerals and How to Study Them i2mo. 

Catalogue of American Localities of Minerals Large 8vo, 

Manual of Mineralogy and Petrography nmo 

Douglas's Untechnical Addresses on Technical Subjects nmo, 

Eakle's Mineral Tables 8vo, 

Egleston's Catalogue of Minerals and Synonyms 8vo, 

Goesel's Minerals and Metals : A Reference Book ibmo, mor. 

Groth's Introduction to Chemical Crystallography (Marshall) 12 mo, 

Iddings's Rock Minerals 8vo, 

Johannsen's Key for the Determination of Rock-forming Minerals in Thin 
Sections. (In Press.) 

* Martin's Laboratory Guide to Qualitative Analysis with the Blowpipe. i2mo, 
Merrill's Non-metallic Minerals. Their Occurrence and Uses 8vo, 

Stones for Building and Decoration ... . 8vo, 

* Penfield's Notes on Determinative Mineralogy and Record of Mineral Tests. 

8vo, paper, 
Tables of Minerals 8vo, 

* Richards's Synopsis of Mineral Characters nmo, morocco, 

* Ries's Clays. Their Occurrence, Properties, and Uses 8vo, 

Rosenbusch's Microscopical Physiography of the Rock-making Minerals. 

(Iddings. ) 8vo, 

* Tillman's Text-book of Important Minerals and Rocks 8vo, 

MINING. 

Beard's Mine Gases and Explosions. (In Press.) 

Boyd's Resources of Southwest Virginia 8vo, 

Map of Southwest Virginia Pocket-book form, 

Douglas's Untechnical Addresses on Technical Subjects i2mo, 

Eissler's Modern High Explosives 8vo, 

Goesel's Minerals and Metals ; A Reference Book i6mo, mor. 

Goodyear 's Coal-mines of the Western Coa-.t of the United States nmo, 

Ihlseng's Manual of Mining 8vo, 

* Iles's Lead-smelting. i2mo, 

Kunhardt's Practice of Ore Dressing in Europe 8vo, 

Miller's Cyanide Process i2mo, 

O'Dnscoll's Notes on the Treatment of Gold Ores 8vo, 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) .8vo, 

Weaver's Military Explosives 8vo, 

Wilson's Cyanide Processes i2mo, 

Chlorination Process. . , nmo, 

Hydraulic and Placer Mining. 2d edition, rewritten i2mo, 

Treatise on Practical and Theoretical Mine Ventilation t2mo, 

SANITARY SCIENCE. 

Bashore's Sanitation of a Country House nmo, 1 00 

* Outlines of Practical Sanitation.^ nmo, 1 25 

Folwell's Sewerage. (Designing, Construction, and Maintenance.) 8vo, 3 00 

Water-supply Engineering. . , t . . . .8vo, 4 00 

18 



2 


00 


I 


50 


4 


00 


I 


00 


I 


25 


3 


50 


12 


50 


I 


00 


4 


00 


I 


SO 


I 


00 


2 


00 


I 


00 


I 


25 


2 


50 


3 


00 


I 


25 


5 


00 




60 


4 


00 


5 


00 




50 


1 


00 


1 


25 


5 


00 


5 


00 


2 


00 



3 


OO 


2 


OO 


1 


OO 


4 


00 


3 


OO 


2 


50 


5 


OO 


2 


SO 


1 


50 


1 


OO 


2 


OO 


4 


OO 


3 


OO 


I 


50 


1 


50 


2 


50 


I 


25 



Fowler's Sewage Works Analyses. nmo, 

Fuertes's Water and Public Health i2mo, 

Water-filtration Works i2mo, 

Gerhard's Guide to Sanitary House-inspection i6mo, 

Sanitation of Public Buildings 12mo, 

Hazen's Filtration of Public Water-supplies 8vo, 

Leach's The Inspection and Analysis of Food with Special Reference to State 

Control 8vo, 

Mason's Water-supply. (Considered principally from a Sanitary Standpoint) 8vo, 

Examination of Water. (Chemical and Bacteriological.) nmo, 

* Merriman's Elements of Sanitary Engineering 8vo,, 

Ogden's Sewer Design i2mo, 

Prescott and Winsiow's Elements of Water Bacteriology, with Special Refer- 
ence to Sanitary Water Analysis nmo, 

* Price's Handbook on Sanitation nmo, 

Richards's Cost of Food. A Study in Dietaries nmo, 

Cost of Living as Modified by Sanitary Science nmo, 

Cost of Shelter nmo, 

Richards and Woodman's Air Water, and Food from a Sanita y Stand- 
point 8vo, 

* Richards and Williams's The Dietary Computer 8vo, 

Rideal's S wage and Bacterial Purification of Sewage 8vo, 

Disinfection and the Preservation of Food 8vo, 

Turneaure and Russell's Public Water-supplies 8vo, 

Von Behring's Suppression of Tuberculosis. (Bolduan.) nmo, 

Whipple's Microscopy of Drinking-water 8vo, 

Wilson's Air Conditioning. (In Press.) 

Winton's Microscopy of Vegetable Foods 8vo, 

WoodhulPs Notes on Military Hygiene iCmo, 

* Personal Hygiene nmo, 



MISCELLANEOUS. 

Association of State and National Food and Dairy Departments (Interstate 
Pure Food Commission) : 

Tenth Annual Convention Held at Hartford, July 17-20, 1906. ...8vo, 3 oo 
Eleventh Annual Convention, Held at Jamestown Tri-Centennial 
Exposition, July 16-19, 1907. (In Press.) 
Emmons's Geological Guide-book of the Rocky Mountain Excursion of the 

International Congress of Geologists Large 8vo, 

Ferrel's Popular Treatise on the Winds 8vo, 

Gannett's Statistical Abstract of the World 241110^ 

Gerhard's The Modern Bath and Bath-houses. (In Press.) 

Haines's American Railway Management i2mo, 

Ricketts's History of Rensselaer Polytechnic Institute, 1824-1804. .Small 8vo, 

Rotherham's Emphasized New Testament , . Large 8vo, 

Standage's Decorative Treatment of Wood, Glass, Metal, etc. (In Press.) 

The World's Columbian Exposition of r8g3 4to, 

Winslow's Elements of Applied Microscopy j2mo, 



HEBREW AND CHALDEE TEXT-BOOKS. 

Green's Elementary Hebrew Grammar nmo, 1 25 

Hebrew Chrestomathy 8vo, 2 00 

Gesenius's Hebrew and Chaldee Lexicon to the Old Testament Scriptures. 

(Tregelles.) Small 4to, half morocco, 5 00 

Letteris's Hebrew Bible , 8vo, 2 2s 

19 



2 


OO 


I 


50 


2 


50 


I 


00 


1 


50 


3 


00 


7 


50 


4 


00 


1 


25 


2 


00 


2 


00 


I 


25 


I 


50 


I 


00 


I 


00 


I 


00 


2 


00 


I 


50 


4 


00 


4 


00 


5 


00 


1 


00 


3 


50 


7 


50 


1 


50 


1 


00 



I 


So 


4 


00 




75 


2 


SO 


3 


00 


2 


Oo 


r 


00 


1 


50 



OCT 1 1808 



